Bear in mind, I am under an NDA and there are things I cannot say, but they're mostly around the specifics of things like exact numbers.
So... I was invited to the Creator Bonus Program at around 1600 subs. Obviously, you can't apply for the Creator Bonus or Early Access program at these sorts of numbers. You can probably guess though, since some comics, like Moth Prince, were taken on at just around 500 subs, that it's possible to get invited on there. In simple terms, if the Tapas staff see your comic and your social media following and they think you're generating good engagement or bringing people to the site, they might invite you on, but if they're unsure, they'll watch and see, and if you can prove them wrong by getting tons of subs, you can apply for yourself.
There is very little that the Tapas staff aren't perfectly open about with regards to contracts. Just as they have said, they will not hold any of the rights to your work, nor will they forbid you posting it anywhere else. They will not necessarily promote your work on the site any more than any other comic that performs solidly or seems suited to the audience though. It's better if, rather than thinking, "if Tapas put me on a program, they'd promote me with features!" to instead think, "If Tapas promotes me with features regularly, that's a sign that they might invite me to a program at some point!"
My contract is pretty simple. If I hit X views per month, I get X money, and then there are tiers where bigger views equal bigger payouts. I can't tell you how much money, or how many views, but I will tell you that the amount of views for even the smallest payout is a big number that at under 3k subs but with good engagement, I don't often hit. So if you think rushing onto a program will be an instant gravy train... sorry, but no. Being on a program has basically no downsides, because it doesn't cost you money, so if you get offered one, I'd advise anyone to consider taking it unless they're angling for a contract elsewhere (for example, I couldn't apply to Hiveworks while on the Tapas program because the contracts would clash due to Hiveworks' requirements), but understand that if you don't have extremely good engagement, it won't pay much, even if you have thousands of subs. In other words, don't try to rush up to big sub numbers using sub-for-sub or bots or something; if you don't get the views, you won't get the cash, same as Tapas ad revenue generally.
Overall, my advice if somebody is aiming to be on a program is that you should aim to make the sort of comic that gets features in the "community" tab, same as just aiming to build a Tapas audience generally, really. Fairly polished art, have a style, story and characters that will appeal to the core Tapas audience (mostly female, North American (but use simple, clear English for ESL readers), around 20 years old, reads comics on a phone), updates regularly (say weekly), if you have a decent social media following, that also improves your chances. If you get a feature on the community tab, that's a sign you're on the right track!