Is ok to message other people while building a relationship

I think it's fine. Just because you found one person you like, doesn't mean you have to cut off all relationships with anyone else... What are they a yandere stalker who will kill all your friends/family? Well, even if you just meant flirting with other people, it depends really. You're still building a relationship with this person, so you're not officially together? Then why not keep building with more people, and then you'll know for sure that they may or may not be the best person. When you realize that this one person stands out to you no matter how many others you flirt with, that's how you know. If you desperately cling to one person without even experimenting with others, how will you know? Maybe you're only doing it for the sake of finding someone, anyone.

I think it is ok to message them in the start before your in a full on relationship like before you make your self know to the world that your in a couple or taken as on here. You can always become friends with the others.

yeah. Never sell yourself short. Until you're officially boyfriend/girlfriend it's all fair game. Typically women have a new interest pretty quickly.. why not keep your options open too? Before being committed you can be dropped like a rock for any reason at any time.