Getting a regular longboard to learn is a great idea. However there are a few things you could do that would make it cheaper and easier to convert it later. The only wheels you can find that you’ll be able to buy a pulley for are Orangatang Kegels, Abec11 Flywheels or the Chinese Flywheel clones and the only trucks you’ll be able to buy a motor mount for are Caliber II. Also, since you’ll need space to mount everything under the deck it would be easier to buy a deck that isn’t a drop through.
If you get a top mount deck with caliber trucks and one of those wheels you won’t have to swap out any parts if you want to make it electric.