I agree w/dougall. IME elodea isn't an easy plant in most tropical tanks. There are a couple kinds, most prefer cool temps. Dying plants can cause water quality problems...& those can cause fish problems...especially in very small tanks, there isn't much "wiggle room"...
As for Japanese style, look up Amano "nature" tanks, that may likely be what you mean. They are works of art! But not necessarily for the long term. He (& his many helpers) created amazing aquascapes, there are videos of them setting them up...& of course the many, many finished products, Wow! These are not really what most of us can do but we can use some of his ideas about perspective, etc. His big thing is trying to recreate a slice of nature; a mountain top, a forest stream bed, etc. RIP Amano! He gave us a new way of thinking about our tanks.
I'm not really a fan of the little white river path of sand to nowhere...it's hard to make it look natural, & more importantly, to stay looking that way for too very long if you are cleaning your tank like I think we should...& you'll only have a 10g right? Hard to have room to do all Amano did in much larger tanks. Start smaller with your goals or just try to grow some plants & fish...& worry about fine tuning it into a "perfect scape"...There is no perfect scape!!! Just Amano-worthy?!?! You need to get photo moment...I want my tanks to look OK, more often, with less work, most of the time...
Yes, I'm lazy! I admit that. I will never have an Amano-worthy tank, that's not 1 of my goals...I want a pretty-ish tank, with plants I can grow without too much effort & fish I find attractive & compatible that I can provide for them without too much work. If they breed it's a bonus...a blessing? ...or maybe a curse...or maybe just snacks?
You need to have realistic objectives. We will help you get there in our different ways.
I'm very happy you have a young betta! You'll have much more time with him than if you got an older but longer finned, larger bodied betta. Younger fish can adapt to water conditions more easily than older fish. They often heal faster from injury. Yes, he may change but that's part of the joy of watching our fish grow up! Embrace the possibilities for him, he's a pretty boy!