Keep in mind that unless you have an unusually wide part of beach, you'll have trouble plotting villagers 3, 4, and 5 there (because the space requirements for those plots is much bigger than the usual size). You can always relocate those to the beach later on though!
As long as that section of beach has enough room, you are good to go. I have three houses on the beach as temporary spots until I can start terraforming.
Yep. It's weird, one of my friends has a map that generated with an unusually wide beach for 85% of it. So, while a lot of our maps might struggle to fit a few homes on the beach in select areas...theirs can probably fit a good majority on their beach lol. Though not sure that they actually want all of them on the beach.