1) DS was 18 mths when we moved him to a twin-sized bed. He wasn't sleeping well in a crib & it was a huge pain when we traveled (which was often). When I asked the ped. about when to move him out of the crib he said "earlier is easier." And I couldn't agree more! At 18 mths, DS hadn't yet tried to climb out of the crib & he didn't "know" that he could escape his bed to play around or anything yet. I figured the toddler bed would be moot since it would be yet another adjustment once he got bigger. So I bought the longest bedrail I could find & then I scooted the rocker to the foot of the bed, so essentially he was nearly confined like a crib, but could get out if he needed to. Slept SO much better ever since.
2) didn't need to do research
3) see question #1
4) With DS #1 it just wasn't that much of an issue - he complied quite easily until around 2.5. We could hear him at the foot of the door & most often he would fall asleep there. But I really didn't care, as long as he wasn't destroying his room or coming out of the room. We would just pick him up & put him in his bed when we went to bed. It never really became a huge issue because we didn't make it a huge issue. Things will be different, though, now that DS #1 is sharing a room with DS #2, who is still currently in a crib. I think things will definitely be more challenging on the "playing" front & DS #2 seems the type that he will be out of the bed more often than not. But, you deal with it, knowing it's a phase & not forever.
There was one night with DS #1 that he just would not stay in his bed. It was like 2am & I had recently seen an episode of Super Nanny who dealt with the same issue, only with 2 kids! So for 90 minutes (no joke), I crouched on the floor of his room & every time he got out of bed, I'd put him (not throw him!) into bed. There was screaming, crying, yelling, all from him. But I remained silent, wouldn't give him eye contact while I was crouching, but stayed consistent. I had no idea it would take that long, it was exhausting & frustrating.
But it worked. It was just one bad night & he never tried to push the boundary with the bed like that again.
Good luck!
vic