OK... i understand your worry and ill try to help here the best i can. although if you really want more in depth help i suggest joining the discord server that is dedicated to the game and full of people who also love the game and have poured countless hours into it... i might only have a little over 260, but people there can go up into the thousands... which if you ask me is literally crazy. but anyways, for your fist question on population, there are at the moment two ways to gain pop. you can either get nomads as you've said which only come when you have a criteria of things, and the second which is breeding. nomads requirements as a start off need these things...
-extra or available housing slots to live within
-plenty of food storage and water storage
-a high happiness level within your village
-a well build defense
-a good amount of available jobs for them to take up (most important next to housing)
with all these things nomads should appear at least slightly more often and in larger numbers. but with RNG its not always guaranteed.
the next part with breeding is a more slow method of gaining pop and requires the onset of raising them from being feeble children. the only requirement for this though is just giving your workers time to relax and talk to each other and "mate."
and by day three it mostly matters your play style, but as a vet i say you should at least have a basic defense up, a farm, a stable source of water, some of the refining buildings like a stone cattery and a lumber mill, and you might be starting on housing. you do not need crystal yet in a normal play style and you can go without that until you start getting into magic buildings or building upgrades that require crithillium. other than that don't waste time building those early on. other than that though you could also have a ancillary or some kind of way maker shack or something, but its all up to you. make your own play style and as you get better at the game, just make your style better... other than that though you should go to the discord for more help on village development there.
as for pushing back the corruption? that is a thing i suggest you wait to do... wait for the corruption to come to you and just hole it behind your walls is all i say you need. don't fight it as it WILL win, but just keep it away from you
as for moving to your second map? do that around when you hit id say around 60-70 villagers... or a better estimate is when you don't know where to put them in job slots. other than that its also up to you
and i think that's everything... i hope this was some help to you in some way or another and ill try to fix my grammatical mistakes other time, but there you go...
**to visit the discord there's a link ill post right here as it would be quite nice of you to join us there**
hope this helps ~shade~