“Is there anything wrong for a yeshiva bochur to be makpid on dating girls who are very pretty?”
You mean because you’re a yeshiva bochur that you should be more machmir on good looks? Well, I was very machmir, and so were the Avos.
Also, if you’re looking for middos too, Rav Aron Kotler zt’l would advise his talmidim to marry a girl from a poor family. I did, and never regretted it.