1a) Yes

1b) Very grindy. Every biome adds a new resource to grind to create/upgrade new gear. Solo vs. a group depends. You can split the grind among yourselves but you'll need more of each resource to cover the group. As an experienced player, I never upgrade my gear beyond level 2. The exception to that is max level troll armor which I use in the swamp biome (which may not be the best idea for new players =) )

1c) As stated above, 50ish could sound about right.

2) To be honest, I'd wait until Mistlands is out officially and read what people are saying then to decide if it will still be a game you'll want to invest that much time in. Mistlands diverges quite a bit from the first five biomes and it may not be your cup of tea afterwards.