Luckily for me, time isn't a constraint, It's purely a hobby and I would most likely not do it as a profession (I prefer Pyshical labour to help counteract my somewhat anti-social and lazier hobbies aside from skateboarding).

I do plan, to a degree, but not far ahead or anything overboard, mostly jot down ideas in notepad or in the source itself.

If there's going to be anything added or changed along the way I usually think of it when I need to, if I waste alot of time too many features and things ahead, well alot of them more than likely won't happen for one reason or another lol.

The easiest way to figure out if an idea will actually go with what your doing, is to actually have something right infront of you, already up and running.

Maybe if I was doing this as a profession I might do things differently, but I prefer to keep it as a hobby.