Should i do wedding party proposals at the engagement party?

I wouldn't do the wedding party proposals in front of everyone, since it may cause hurt feelings to people who aren't being asked. Plan a time outside of your engagement party (but while they are still in town) to ask your friends to be in your wedding party.

It can be better to wait until closer to your wedding to select the wedding party since many things can change, especially having a wedding more than a year away.

Not at the party! That leaves a lot of room for hurt feelings from those who you aren't asking.

Either have them come early and do it before, or find another time during the weekend