Hey man. Thanks for trying to stir the pot and get in the theme circuit. Here's some quick answers to your questions.
a) Themes don't fill up instantly - the very best ones take days to fill if not a couple of weeks. The quickest one in recent memory was my first Over the Hump league which filled in about 2.5 days. The continued versions take longer and longer to fill. The renewal of the EOL filled in 4 or 5 days which is amazingly fast these days.
b) $77M cap is beyond ridiculous. You can build pretty much the most dominant line-up in the sim for less than $60M. At $77M you're just wasting money on minutes you'll never use. Thus the most serious of sim players (which IS the theme circuit - i.e. the people who actually play the majority of themes) usually disregard these high cap leagues. If you want to do a high cap league that is somewhat challenging AND will encourage roster variation, look at doing something in the $50M - $54M range. Otherwise, you're going to see Wilt-Ben-Worm-Jordan-Lebron in at least 3 or 4 teams (and then Wilt-Dwight-Worm-Lebron-Kidd in another 2 or 3) with the finals consisting of those squads. Even in the low $50M's you'll see a lot of the same line-ups. So if you really do want to do a high cap league, I recommend doing high cap + blacklist (Wilt, Worm, Jordan, Lebron, Kidd being the biggest targets followed by Big Ben, Dwight Howard, Moses & Barkley).
c) You don't specify rookies, clones or WW in your advertisement here. I recommend saying no for all three. Most owners hate rookies at any cap level, and with this being a high cap league, there's even less need for them. Clones suck major donkey balls at high caps because imagination goes even further out the window (Wilt - Worm x3 - Lebron x 2). And the WW is again something not needed (in any league, but especially in higher caps).
Good luck with your theme, man. I highly recommend refining it a little bit and being more detailed in your advertisement - I think you'll see better results.