All great advice - especially the stuff about being patient and only buying stuff because you like it, not because it will be worth a lot.
The general advice I have kind of combines those: Spend at least a few months on the sidelines before making ANY purchase other than maybe a loose figure or two. I made so many purchases over my first year or so that ultimately didn't really fit with how and where I wanted to collect, and then I had to sell it on. It would be wise to spend a few months seeing all that is out there before going on a spending spree.
Also, general advice I would give (which took me a long time to figure out - I am still learning) is that if you should focus on items that will stand the test of time. That means avoid all ESB 31 back and later (through POTF, Ewoks, etc.) MOCs that have yellowed to a significant degree. The yellow, brittle bubbles are a ticking time bomb in my opinion. Focus on clear bubbles (although don't overpay!), loose figures, card backs, proof cards, etc. Stuff that will last and look as good on your shelf in 12 years as they will in 12 months.
Also, don't pay too much for any sealed MISB items. The tape has come off too many of those to justify the premium ascribed to MISB versus MIB in my opinion.