$X Basic / $XX Premium / $XXX Ultimate - having such pricing? What's the percentage of subsrciptions of each?

As long as you
Basic = ((Cost of operating the start-up monthly+ Fund to reinvest and grow next 2 months)X2) / Number of expected users.

For example,
If I am expecting 1000 basic users, and my monthly operating cost is $2000 and the next 2-month expense for growth is 5000 then the basic should be.
((2000+5000)*2)/1000 = $14 monthly.

And $/$$/$$$ ratio, in my opinion, should be such as user sign up for $$. Means $ should have few features with free 2 weeks sign up. $$ should be a lot more feature with a slite increase in cost like only 20% cost but 50% more value and finally $$$ should be at least twice the basic.

I hope it helps. If I knew what your app is I could have answered better.

It may very well be closer to 99%/1%/0%