I would only send a son to a serious yeshiva that has an excellent hashgocha and own dorm. For me it was very important that my shvere lives in Eretz Yisroel so he was able to “keep an eye” on my son too. It also gave my son a good feeling to know his zeida was close by.
Ask typical questions – What happens shabbos? does the yeshiva provide meals?
every day Suppers?
Is there proper supervision at night? Till what time are bochurim allowed out at night?
Hatzlocho