Wow, brand new owner taking on 4 teams at once!

Here's the thing, much of the engine, given time, and patience can be broken down into fairly predictable patterns. Pitching however is very tricky because of all those moving parts Mike mentioned. You have identified a lot of the important variables that are player specific. However, in any given player assessment, you'll also need to look at the defense behind him and the park he plays in, sometimes even the world he plays in.

I would start by looking sorting through successful pitchers in neutral ballparks across multiple worlds to see what traits they have in common. Make sure you focus on players with more than a season or two under their belt. Once you get a feel for that, you be able to branch out to other players to see why a pitcher with good ratings may underperform and a pitcher with sub-par ratings outperform.

Good luck.

"Wow, brand new owner taking on 4 teams at once!"

Yay!  Rookie mistakes x 4!

Agreed with Mike that you left out pitches and durability which are also important.  It's very difficult to say "this is the minimum" because many guys won't take anything less than 50-55 control (widely considered most important) but I've used guys with 50 control if everything else balances it out.  I used a reliever with 51 control but he had a 99 Gb/fb (so he walked a lot of guys but got a TON of double plays) and he also had 80's velocity too (lots of strikeouts).  His splits were in the 70's but he had two pitches, both over 85 which is AMAZING for a reliever. 

Here's a few random pitching rating tips I use.

1) Splits, control, and pitches (not necessarily in that order) are king.  A low rating in any of those can be balanced out by high ratings in the other two.

2a) A SP should have at least 3 pitches, but many believe that 4 pitches is better than 3, and 5 pitches is better than 4.  Some will tell you that even if the 5th pitch has a rating of 27 that's better than only 4 pitches. 

2b) As for pitch rating, a good Starter will have at least 2 pitches better than 75.  A really good starter will have one pitch over 85 and one pitch over 75.  A potential dominant starter will have 2 pitches over 85 (but remember, this can be negated if his splits and control are mediocre).  A good reliever (closer or ace setup man) definitely needs at least one pitch over 90 and a second pitch over 80.  It's extremely rare to see a reliever with 2 pitches over 90 but if he has 1 pitch over 90, he is a potential closer (again, depending on control and splits).

3) High stamina can be decieving if the player has lower durability.  I don't like starters with 80 stamina and 17 durability.  Stamina relates to higher pitch counts and durability is how quickly the pitcher recovers between outings.  So the 80/17 guy could easily throw 110 pitches but he may still only be at 88% 5 days later when he's due to pitch again.  I prefer my starters to have Dur of at least 22.  If you want to use a starter with only 65 stamina then he's going to need at least 30+ durability.  

4)  HEALTH IS EXTREMELY IMPORTANT FOR STARTING PITCHERS.  I have noticed, and I believe many will agree, that injuries to pitchers are both more frequent AND more legnthy than injuries to position players.  Pitchers are more likely to blow out an elbow or shoulder and miss the entire season.  For this reason, I feel nervous if I have a Starting Pitcher with health of less than 75.  I set the bar very high for these guys since I depend on them.  I have no problem with a 59 health LF but a SP with 70 health scares me, especially if he's All-Star caliber.  

5) Do not use your best relief pitcher as your closer.  A closer will typically get 45-60 innings in him, depending on your team and how you use him.  A decent Setup A could easily throw 90+ innings depending on his stam/dur combo (more like 70 IP if he's at the lower end of those ratings).  In order to leverage your best relief pitcher and maximize his IP, use him as SuA and use your second or third best guy as your closer.  I've been known to use a rotation with 3 SuA guys and not even have a closer designated.  That way the AI will choose one of my 3 SuA players to close every game (closer by committee).  This rotation works VERY well.

6) Do not depend on LHS or RHS (specialists).  The AI for these roles sucks and they will rarely ever pitch.  If the player in this role is good enough make him a SuA or SuB, if it's a guy you don't want to throw very often anyway then it's probably ok to leave him as LHS or RHS.

Any more questions feel free to sitemail me or ask here to get a few more opinions.

Durability is often overlooked.  15 is as low as I'll accept for a starter.  If a guy has a durability of... 2, 4, 10 like you'll see from time to time... no matter what the stamina he should only be used in relief.

Some very good points in here. One of them was a guy with 65 stamina needs to be 30+ in dur. Again here is an example that any combo can be successful. He threw 185 innings in his first full season and won the Cy Young.

I'll use a DUR as low as 17 in a SP (as long as the STA is above 80), but you have to lower his PC so that he doesn't need as long to recover.

A late inning RP is typically high dur, low sta.  But there are plenty of pitchers with fairly low numbers for both (in the 30s).  These guys make perfect closers, since they top out at about 50-60 IP per season.  Example:  Heath Rollins

Please keep in mind that these are individual beliefs.   I was told my "long relievers" didn't have much value on the trade market.  I won 109 games and the WS by giving double digit starts to pitchers with stamina of 65, 62, 64, 73, 67, 58.  Only two of them had a DUR over 25.  I had two other pitchers get 7 and 9 starts.  Under 25 DUR/62 STM.

Yes. Almost anything the forum is individual belief, this isn't the hbd Bible. I will add that You can get away with multiple starters with 60ish stamina if they at least go 5 innings almost every time and you have a good bullpen.

Of my 2 teams, my Tampa Bay team has starters that go 6 or 7 innings pretty much 90% of the time. I can get away with low stam and during relievers. My Helena team has one guy who led the NL in IP and of the 11 other pitchers 9 of them have 60-70 stamina. My starters don't throw as many innings in Helena so I go for high innings relievers.

>>5) Do not use your best relief pitcher as your closer.  A closer will typically get 45-60 innings in him, depending on your team and how you use him.  A decent Setup A could easily throw 90+ innings depending on his stam/dur combo (more like 70 IP if he's at the lower end of those ratings).  In order to leverage your best relief pitcher and maximize his IP, use him as SuA and use your second or third best guy as your closer.  I've been known to use a rotation with 3 SuA guys and not even have a closer designated.  That way the AI will choose one of my 3 SuA players to close every game (closer by committee).  This rotation works VERY well.<<

If you have multiple good reliever, the non-closer roles can work out VERY well.  I'm currently using that on two of my teams.  This would work out well in the bigs too if people weren't married to their roles and managed to a statistic (the Save), but I digress.  In HBD, the multiple SuA option works very well and you can squeeze a lot more innings out of your better pitchers.

My number one setup guy in Moonlight Graham almost 200 innings this season.

Thought I'd resurrect a very informative thread for those smart enough to listen. (A sincere thanks to all the contributors!) Allow me to pose a related question. I've wondered if the velocity rating should be treated just like another pitch rating. So if you are looking for an SP with at least 3 decent pitches and you see one with only two, but he has a good velocity, you might treat that as a 3rd decent pitch. Or is that all a bunch of hooey and I should pretty much treat it as a second-tier rating for pitchers?