How much is need for 10/20 Nlh I am a reg 2/5 player that came into some $$

What are you trying to accomplish? Playing for a living, recreation?
How much do you plan on buying in for?

If you're playing for a living. I probably wouldn't want less than 100k.

If you just want to have some fun and take a shot then 10k should be fine.

Move up at br150 but cashout 125, does that mean earn 275 at nl2? And so on and so forth through the stakes?

Now I see the key, so once $110 is earned, you cash out $31 and leave $79? Then grind up the br to $120, down to br89, wash rinse repeat?

Personally i just like to have at least 35BI for a level to feel comfortable, but really depends on you tbh

what exactly is the point of cashing out 50 stacks on each limit?
Is this for NL2 Pros who need the money for a living?...

I guess it just shows how to grind through the stakes and bank a profit..

what i need a bankroll to play 3,5 hu regular speed sng?

The money being cashed out could also be used for poker playing related expenses.

A database, HUD, affordable training site, better mouse, better monitor. Those are just a few things that might make sense during those first few levels, assuming you're winning, enjoying the game and plan to play a good amount in the future.

The bankroll required for heads up sngs depends greatly on your winrate.

Some other variables: Ability to move down, your comfortable risk amount (IE, if you don't plan to keep playing after losing 30 buyins, then you don't need to plan for situations that involve you losing more), future goals, ability to replenish bankroll, cashout plans.

A general rule of thumb is anywhere from 30-75 buyins. But a successful player that can move down during a bad stretch without chasing losses can take shots with as few as 20 buyins. Other pros that consistently win sometimes like to keep at least 100 buyins in their online bankroll, though I'd personally consider that overkill and I've seen a lot of fear-comfort weaknesses developed from people who insist on having a huge cashier at all times.