Alright I'll do my best.
1. So I'm pretty sure you do have to break an altar for natural mech boss spawns, including enemies dropping summons, but if you can make a fishing rod, then you can still gather the ore necessary to craft the summons.
2. Corruption is easier to cordon off cause it's all straight tunnels down, crimson is better for early arena building due to the big open cave, so take your pick.
3. I'd say medium, large can become annoying and small makes too few chests, and arenas harder to make without constantly killing your npcs or entering space and getting low gravity.
4. Sky fishing starts when the music changes to the space theme. On medium and small worlds, it's very unlikely to get an island below the boundary line.
5. Yes, but it's incredibly lucky if it happens, just relying on world generation for that.
Hopefully that helps? I'm not an expert on this stuff but I do know an unnecessary amount of information.
What is the challenge you're thinking of doing, anyway?
For any terraria players. I'm going to start playing the game first time tomorrow
In order to see if a self imposed challenge idea i have can be done on the for the worthy seed and potentially get fixed boi
So, is it true their is a chance of a bomb dropped by shaking trees in those 2 seeds? If so what is the chance?
And do i really need wood for much before i can get the dryad? Seems can make a workbench out of cactus and bamboo for instance.