I choose not to handle my Leo very much, but she still doesn't bite when I do have to pick her up, though she is a bit jumpy and certainly doesn't like being lifted, though she's fine just sitting on my hand or arm because it's warm. The only time she's gotten upset with me was when I was having a hard time getting skin off of her toes so took a very long time, longer than I should have. But if you want one to be really comfortable with you short handling sessions on a regular basis would be good. I got mine from petco or petsmart 8 years ago, started out with a 10 gallon then upgraded to a 20L when she was an adult. I think a 20L would work for a young gecko, just so long as you don't leave a lot of open space where she would feel exposed and you make sure she isn't having trouble finding her food. If you feed crickets I'd watch and make sure she gets them all so they don't make a snack of her later. I started out on the wrong path with my Leo (don't listen to the people at petco), had calci sand, no supplements, no gutloading, no humid hide (and she's lost a lot of toes because of that), a tiny UTH that I stuck to the side of the tank plus a heat lamp, it was just all wrong (and I was only 12). I'm lucky she even survived. So she's not the most well developed little Leo out there, so just to make sure you have all of your bases covered:

Gut load your feeders-I have my mealies in corn meal and oats, plus the wheat middlings they come in and cricket gutload. Then I give various veggies for water.

Have a Under Tank Heater under the tank, should take up half the tank floor, you probably need a thermostat for it

They need pure calcium in a dish as well as calcium with D3 and a vitamin supplement which you dust on feeders

They need 3 hides, one on the cool side, one on the warm side, and one humid hide (I put it on warm side)

Need probe thermometer or temp gun to measure temp of substrate (not air), temp should be around 90 degrees F on warm side

No loose substrate, Lots of people like tile (preferably textured) because you can get natural looking stuff. Some people use shelf liner. Repti carpet is better than sand, but I have heard some Leos get their nails caught in it plus it's not easy to clean.

Good luck with your Leo!!