Welcome, ValerieAnn. Good for you for getting out and trying. Ask, away.
Based on your height, you definitely would be in a small frame or even an XS. As for using inseam for a fit clue, use your bike inseam, not your pants inseam, as per Surly bikes:
"(Make sure you are referencing your "cycling inseam" and not your pants inseam: Stand with your back against a wall, your bare feet 6" apart on a hard floor, looking straight ahead. Place a book or carpenter's square between your legs with one edge against the wall, and pull it up firmly into your crotch. Have a helper measure from the top edge of the book to the floor. (You can convert inches to centimeters by multiplying inches by 2.54.) Repeat two or three times, for consistency, and average the results to get your inseam length."
One leg shorter than the other is also solvable. Maybe use a sole implant in the shoe and so on. As for the foot slipping, that can also be solved by taking some of your weight off the seat and shifting it down to the pedals on a downhill run or just getting a different style of pedal. All in all, though, I think it's best to just get on the bike and ride a little bit, daily, and work up to longer rides, slowly, as you have been doing.
Joanie