If you are serous about gaming and you have an army in mind, then it is debatable whether oyu should buy Mines of Moria unless your starting army is Moria Goblins. This is because the Fellowship aren't useable as one generally in battles and with the hefty price tag attacthed to Mines of Moria you could get a couple of boxes and blisters of whatever army you decide to collect. Then you can generally find a cheap rulebook on Ebay as there is small one that comes with Mines odf Moria tha tlots of people generally sell off.
However if you are looking for an introduction to the hobby then buy Mines of Moria as it contains everything you need to get started, especially if money is not too much of a problem.
I've been playing LOTR 7 years but I've recently taken the plunge into 40k, as 40k seems to be the system that recieves the most support of Games Workshop (although the whole place hads gone Warhammer mad at the moment).
You also need to take into account whether you want to start the skirmish game (strategy battle game) which is barely supported anymore but is the most commonly played system around here. Or WOTR (war of the Ring) which is a much newer game which recieves quite a bit more support but is focused on large armies and units, it is easier to enact very large battles with WOTR. Whereas the Strategy Battle game is focused on indivduals and has alot more scenarios and storytelling involved with it but it is still possible to do large battle, but the time taken is much longer.
Whichever system you choose, just don't expect the money in your wallet to stay there for long...