1.) Deck size: Okay, this is pretty subjective these days, it appears. Back when the game was still being played in paper in tourneys, you would have been hard-pressed to find a deck clocking in at 40/40 or more. The only decks that really used that many cards were things like Dwarves/Moria decks that were designed to cycle through the deck very quickly via card draw, cards that were immediately playable in fellowship phase and thus didn't need to be kept in hand, and cheap minions that could easily be played and recycled.
Since you mention that you are an experienced MTG guy, I'll say this: card advantage is much easier to come by in LoTR tcg than it is mtg. You are not locked into one or two cultures to have good cycling tools like you sometimes can be with such cycling and card draw in Blue and Black in magic. The other thing is obviously that you reconcile your hand frequently, so playing cards that say "Draw a card" or "Draw X cards" aren't quite as valuable to you in LotR as they would be in magic because the game's design in and of itself frequently refills your hand.
While some others may advocate playing a great number of cards (50/50 or something like that), in most cases these players are more seasoned and are probably running various tutors to fetch out bullet cards (kinda like Melira Pod in Modern format magic, if you are familiar). I, however, as many old school players will, would urge you to stick to 36/36 or even less. I find 32/32 is typically best (lower number like this are typically better for shadows like Nazgul), though going higher if you are playing a swarming shadow (like a Moria Swarm in Fellowship block) is okay. When it comes down to it, the best way to tell is to test. I had a knights/besiegers deck that was doing terribly and having trouble with cycling at 34/34 but I trimmed two cards from each side making it 32/32 and it made a world of difference.
Like Magic, running a 4 card playset of cards you want to see early and often still holds. If you have some tutor effects or a card is unique and you don't want to see a bunch of them, then maybe don't run 4 but rather 2-3. Having a way to cycle unneeded unique cards is helpful as well.
2.) Strategies.... In Fellowship block, all shadow cultures appear to have some success. Moria Swarm or Moria Archery, Uruk beatdown with
Keeper of Isengard and
Savagery to Match Their Numbers, both twilight and non-twilight nazgul... It just kinda depends on what you wanna play or what you feel has synergy with your freeps side. Maybe you are playing a choke frees and are concerned about being able to double move. You could pair that will a shadow designed to stop you opponent (something like Uruks or Nazgul are good for this... Drop a
keeper of isengard and dare them to double with twilight left in the pool) or perhaps be content to single move and play a shadow geared more toward killing the opponent (Swarm 'em out with Moria or Grind 'em down with Sauron wounding with things like
Hate and
Orc Bowmen). If you have more specific questions about strategies, I can try to answer those as well.
3.) This is a bit tougher to pin down... Its not quite like in magic where if you are running red in modern format, then you obviously want a playset of lightning bolts in your 75 somewhere. The various archetypes determine what the key cards are for you. I'll try and list a few of the general "good choices" that could be included in a variety of decks.
General Freeps:
Aragorn, Ranger of the NorthElrond, Lord of RivendellOttar, Man of LaketownStingPower According to His StatureLegolas, GreenleafGandalf, The Grey PilgrimSam, Son of HamfastBoromir, Son of DenethorAragorn's BowThrarin, Dwarven SmithAny possessions for the main freeps characters in your deck (
Ranger's Sword for your Aragorn,
Blade of Gondor for your Boromir,
Asfaloth for your Arwen, etc.)
General Shadow:
Ulaire Enquea, LoMTower AssassinThe Balrog, Durin's BaneBill Ferny, SSFGoblin RunnerI should mention that most of the companions and minions listed above could be considered what are called "splash companions." In the same way one might splash a color in a magic deck for the use of a spell in the mid-to-late game, these companions/minions can be thrown into a variety of decks and provide value even though they don't necessarily synergize with the overall strategy of that deck.
This is by no means an exhaustive list, but I hope it helps. I'm also happy to try and field any further questions you may have or clarify anything I have stated that is a source of confusion. I admit my proof-reading skills leave something to be desired at times.