1. You can tell her you don't like something if she asks for your opinion. I know it's hard but any tackiness would reflect on the host, not the guest of honor.
2. What ECB said is 100% correct - inviting men could effectively double the guest list. If your friend can't afford/fit that many people in the space, that's a no.
3a. YOU aren't sending the invitations, your host is.
3b. People RSVPing and not showing up happens, it just does. I was at a wedding last weekend and had two empty seats next to me and there were scattered empty seats at other tables where people had RSVP'd and not attended. It's not avoidable completely. To get the best idea of how many attendees there will be, your host should set a response date a week or so before the event and then call anyone who has not RSVP'd to check in with them. They might have forgotten or lost the contact info. Again, this isn't anything YOU should be doing. Have a list of phone numbers ready to hand over to your friend if she needs to touch base with guests.