So what's a good place to step into this? And do I need to buy walls and walls of figures to play, or could I get by with just one or two if I wanted?
You could probably do just fine playing with Swap Force although the other games are pretty fun. Essentially to unlock everything in every game, you'd need:
One character of each element (Fire, Water, Magic, Life, Tech, Air, Undead, and Earth). If you get ones from the first game, they can be used in the next two games, so those are probably most beneficial to get. (S3 are what the reposes are called in Swap Force). With the first game pack, you have 3 already (Magic, Tech and Water) and it should be easy to nab the rest from other triple packs and such.
One Giant character (Giants pack comes with Tree Rex, also of the Life Element)
One of each of the 8 Swapper "Abilites". With Swap Force, each of the Swappers bottom half has an ability. Wash Buckler and Blast Zone are Climb and Fly respectively. Currently, all should be available although the Stealth one (Stink Bomb) just came out and will probably be super hard to find.
You'll also either need one of each element Swapper or a second controller for whatever system you buy the game on. There are "Dual Element" gates that you can either pass through with a swapper of that element or if you have 2 individual characters playing at the same time.
That'll ensure that you can get 100% in the game and unlock every single area. Now, you don't need to in order to progress but I enjoy going back and hunting down stuff im missing. You can easily just keep your starter pack characters and just never buy another one. It's also beneficial to just pick out your favorites unless you intend to collect them all. I had picked up one of all the characters from SSA and Giants (Giants was mostly assisted by JC Penney's giveaway stuff last year so I got a huge chunk of my collection completely free) and for Swap Force I figured Im not gonna do that and just collect the ones I really like.
Does anyone else know how to add the characters to your digital collection? We own around 20 characters, but if i go into the game it only shows as having 9 in my collection.
The characters I believe should be auto added to your collection (since in Giants you had to manually take ownership of them). You might have to go into the individual character and select manage and see if you can take ownership from there. If you have multiple save files, that could also be the problem.
I dunno if you might be talking about this one instead, but I had registered about 100 characters and they all up and disappeared from getting stars in the Portal Master Rank. They're still visibly there but the game doesn't recognize anything that I had registered, and bumped my rank down almost 9 levels. (because I just had so dang many lol) Not that it's a big deal because you can earn stars in other ways (and now new characters register just fine) but i feels bad that huge chunk of my collection is like not anything.