First off, reducing your buy in doesn't reduce your variance (bankroll management is still maximum buy ins). The shorter your stack the lighter you have to be willing to play for stacks, once the pot:stack ratio gets low willingly deviating from optimal strategy is like denying gravity and optimal strategy is high variance.
You also wont notice a skill difference.. ok, you might, I have no idea what the play on the 40bb tables is like but the play at 2nl is by anyone's standards truly terrible (seriously, an actual monkey with a hand ranking
chart would have edge).
Buying in for 50bb wont put you at a disadvantage to the rest of the table because they all have 50bb too (smallest stack is the effective stack, either player having more makes no difference), with that being said, buy in for 100bb, it's better and there's no valid counter-argument provided that you have an expectation of winning (I'd play it even if you don't so you learn the right skill set).
So yeah, play the 100bb tables and keep your stack at 100bb or more.
You only have 10 max buy ins, which admittedly means your chance of going bust as a new player is high, play like a nit (so you can't make mistakes as easily) and you'll be fine. If you can limit your mistakes which increases your edge, 10BI is enough.
Alternatively, learn to play SNG's which offer smaller stakes and you can stick to safer bankroll management with them.