as a prefered player you get 6 toon slots....but you can increase that as much as you like with slot unlocks....when i let my sub lapse i go from 16 down to 8 (bought 2 slot unlocks so i can have one of each class when between GTcards.
you can make preferred play very cloase to sub play via CC or off the GTN...about the only thing you cannot change is 1 item per mail when sending, no sending credits thru mail, max of 3 crew on missions/crafting and only craft 1 item at a time per crew member.
Hmm, I didn't realize about the crafting restrictions, I knew about the 1 item and no credits thru mail. I did purchase a couple of crew unlocks, but I thought they were to be able to do the various jobs...I see what you mean now about the crew doing 1 item at a time, and only 3 on the go. I suppose I can live with that. As someone else mentioned, for only basically running dailies or the odd reputation event (most of which I've finished), I probably won't notice a huge dif, because I'm done everything else.