Not a Tourney player here but, if I recall correctly you want to have a minimum of 100 Buyins as bankroll for these games. Sticking to your BR-Management is the first step to become a profitable player. Hence you would be allowed to play games up to 0.5$ BI.
As a rule of thumb, the more players in a Tourney the higher the variance, so if you are still learning and don't know if you beat the games I would recomend 1 table SnG's. This will also teach how to play in later stages of MTT's. Wich require different strategies for the different stages of the tournament.
In terms of softness I would say in this BI range there is not much difference between SnG's or MTT's.
Much depends on your knowledge and skills. Tournaments on the PS have a large number of participants and it is harder to get prizes there. I would recommend inexpensive SNG, single, double table SNG, as well as 45 and 90 people. Over time, start playing for 180 participants, and then try MTT ....
I advise you to play with 50$ on pokerstars multi-table tournaments 0.25$ for 45 and 90 people in the future, when you earn at least 100-150$ you can play MTT 0.55$ as an option, you can Deposit this money to another poker room and start playing on the MTT bankroll with 0.11-0.22 $ so that your risks of going broke are minimal
I would avoid MTTs for now though if you can, as if you use 100buyins as your BRM you are playing the 50c MTTs and on PokerStars those games get several thousand runners every game and therefore is difficult to cash regularly.
It depends on what your level is and what u played in the past.
Cash games is a good idea if you are a good player.
But in case you're just starting out, play sit and go.
Tournaments u need more buy ins
I think its better to play sit n gos, you should have lower variance on those games as opposed to MTTs, which most of the times have larger player fields.
The higher the variance the game, the more diversification you need in other to lower the risk of busting your bankroll