with 100$ you are rolled for 5nl.
I've made the switch myself way to many times between cash and tournaments, but I guess you just have to find out what suits you best.
first of all, cash games are indeed more about post-flop play, and pre-flop all-ins are very rare because of the deep stacks, so usually when two people go allin its KK vs AA,
This means you should drop hands like TT/JJ pre-flop in some situations, which is way less common in tournaments.
Are you looking to play 6max games or full ring?
If you play full-ring it's pretty much the same at these 2nl and 5nl, you have 3 types of players:
1. complete idiots (here's your money )
2. (mostly russian) nits that play 20 tables, They are allll over the place, it's really horrible,
This makes micro stakes so damn boring, I've grinded 5nl FR for a really long time and it made me almost quit poker, You'll see these people all over the place, playing 2/2 to 10/10.
3. TAG's. These are very rare and play 14/14 - 20/20. These are the only decent players in these games.
So if you don't like the tight play, don't play FR, it's a nit fest.
I suggest playing 6-max on stars (I prefer stars because of the UI and VIP-program). Playing 6-max you'll learn faster, and it won't turn you into some kind of zombie-nit.
Another option to start out may be Ipoker (altho I hate the software, again, this is a personal preference).
You could play the 5nl HU there, heads-up is definetly the fastest way to learn, and it's pretty fun too,
The rake is killing tho, so making a profit might not be as easy at start, but at the bright side, 99% of the players there are complete idiots.