So I'm finally sitting down to play this over the chrimbo hols.

I've been down the Dead Nations, Spoke to Pharod, hooked up with Annah, and now? Back in the Hive.

I held off all the Dustmen quests as I was uncertain of whether, if I DO go through with the quests, does it lock me out of joining another faction?

In any case I did the quests at the point i'm up to now. Got to the final question. Do you want to join? or Not? So I picked no, hoping the offer will still be open. But it's not. No worries. Save Scumming.

My question is, if I do elect to join the Dustmen, will I be locked out of other Factions? Factions I'm still yet to meet and learn about? Will I get another chance to join the Dustmen if I pick "No?" when being asked to join? Can you swap in and out of factions?

Please be wary of what you say. Do not elaborate on other factions. Thank you.

You can easily break off with one faction and join another.

Joining a faction does not prevent you from later joining a different faction. Joining another faction will sometimes require that you relinquish your previous faction affiliation (after which you usually won't be able to rejoin that faction), but there's never a case that you won't be able to join a new faction due to a previous faction affiliation.