Just my two cents, but if I were you I would first do a few 'crops' in soil. Then if you want to move to hydro, do it.
This allows you a huge amount of leeway to study how a plant grows, it's cycles, what it is supposed to look like, etc. in a relativity forgiving environment.
Then move to hydro where there is very little leeway for error and is more precise. From your experience with the soiled plants you will be able to tell right away if something isn't right and can make the correction before it is too late.

As for the light and two plants...
Indicas have a tendency to be shorter and so the light can reach the branches better. For two plants, I would just use a 250 to 400 watt.
I would step it up if I was growing tall plants like Sativas. For two plants I would most likely use a 300 to 400.

If you think you will step up the amount of your crop, then get the more powerful one so you don't have to buy another light and more bulbs which are very, very expensive.

Personal experience as I said. Take for what it is worth. Good luck.