That buying guide on TFTC is really a great start point....i started buying in last year in "order of release" but sort of wish i had not been such a slave to my "completist" tendencies and just bought what appealed to me in terms of LOTR lore (like i dig Silvan stuff way more than Dwarves)
Searching out stuff on ebay and BGG marketplace has been a good way for me to find people dumping large amounts of cards for way below the retail price.
also check out Seastan's "Minimum Purchase" play-throughs on YouTube to get an idea of what can be done with a 1 core set and some expansions. the guy is a total genius. here's one of the videos: