It's entirely up to you. In 5k that kind of layout doesn't have much disadvantage over a spacebar based layout. However, if you plan on learning 7k later, it might be a good idea to stick with the spacebar. It's certainly possible to be good at 7k using something like sdfghjk, but that layout requires a pinkie on one of your hands, and pinkies are much weaker than your other fingers, which puts you at a disadvantage.
In any case, it's totally up to you. There's no 'right' way to play mania.
In any case, it's totally up to you. There's no 'right' way to play mania.