Have your cambodian visa done before you get to the border. You can get it there but it makes you a tout-magnet.
I wouldn’t worry about the gender thing - you’ll be right in that part of the world. The Angkor temples are well worth the trip.
We did the bus from HCMC - SR. Bit of a sh!t as its long and you’re often hungover, but not thaaat bad. Guesthouses are a dime a dozen and range in quality - there’s no real good way about it though. Check out TripAdvisor if you’re concerned.