Personal opinion only:
1: When your games of set 1 get boring/there aren't any new strategies you want to try, it's time to add set 2.
2: I would add sets 1 at a time vs adding 2 & 3 at the same time. (Product for 2 is cheaper than 3 anyway, so that should be easy to do)
3: There were some balance issues when set 1 came out. The most noticeable results were creating the rule of 4 and issuing errata for
the Mirror of Galadriel. I'd start with all errata in effect and the limit on drawing 4 cards in the fellowship phase, unless you want to play a few games without them and see how broken things were. Also, much later they added a rule that you can't cancel the ring-bearer's skirmish. I would ignore this rule because it was created for alternate ring-bearers, which don't show up in this block
4: I'd ignore them until games get boring because some decks are OP, then implement them