I don't really like micro transactions.
I hate them too. Everything is available to you without buying with a few caveats.
Items are given out randomly and given for gettting certain achievments to pay and non-paying people. That might mean that the item you really want might take some time to get but you can get it for free.
The free version is limited to only 50 items. Now this is a lot of items but there are many more in the game. You can delete some if you want to get others.
Free members can't initiate trades to get new items.
Hats don't seem to randomly drop but they don't effect gameplay at all.
With any purchase no matter how small you get bumped to the paid version so it costs as little as 50 cents. Whenever Valve can sort out their problems with me paying I'll do it once and get bumped up.