Does anyone have any specific advice for using a 2-Man rotation @ 80M Cap.

Is it better to go 1, 2, Tandem 3-4 than a pure 2-man?

I am trying to find a way to go 2-man for $25M then use $12-15M on relief. Is this even possible?

I've had some success with lesser pitchers like 1886 Dan Casey, he's over 500 innings for $14.5M. You probably won't do well if you spend less than $33-35M on your entire staff. You can mix match parts to get the innings you need. A 2 man staff isn't difficult to manage, but some early exits will tax your bullpen. Draft accordingly.
If you do go with a 2 man staff, pay attention to their real life IP/G number. If you skimp you will need a beefy bullpen to get you there...
Any number of starters will work, just have a plan...tandems are a good way to utilize those tweeners. In a 3 man I use the 95 inning Roy Patterson starting ahead of the 200 inning Kid Madden. Make sure to set pitch counts. Beware the learning curve...

Once you figure out how to utilize innings you can make any type of rotation work. You are drafting the number of pitches available, not innings. This is math, not baseball. Elbirdo's insights on fatigue and how to figure pitch counts are gold. Find them in the FAQ Pinned threads.

You can now set a SP to go as few as 20 pitches. Use this as a way to bring in your would be starter in after a low IP guy. This can be extremely useful to a guy on the fringe of having enough innings to fit the 2 man scheme, like the 413 inning Joe McGinnity. Dropping 50-100 innings in ahead of him can be effective. Set him to be available Inning 2.