It seems like you're off to a good start. Having your enclosure and equipment up, running and dialed in is definitely a huge plus in your favor. You're saving yourself and your new pet from unnecessary stress and headaches. So good job there! .
I've used and still use both front opening top opening enclosures. I prefer front opening, but that's more personal preference. I've never noticed a difference in ease of getting the snake in and out either way.
A 10 gallon will work perfectly for a starter enclosure. Just make sure you've got at least two hides and a decent amount of clutter (fake plants, etc...) for security. It also helps to "black out" the sides and back of the enclosure with cardboard, construction paper, foam board insulation or something. Just make sure it's on the outside of the enclosure.
Lastly, when it comes time to actually choose your snake do yourself a favor and buy from a reputable breeder. Avoid pet stores and "flippers" who just buy and sell the animals.
Good luck. Don't be shy if you have further questions.