It depends on the artist to me. If I'm a huge fan of someone, then I'd like to see maybe a sketch or something every once in a while. Just so I know they haven't fallen off the earth yet. But I'd rather wait to see a masterpiece that they took time, patience, dedication, thought, passion and stuff to create. Those are the artists that I really admire. And you're one of them. So if I don't see anything for a while, I know you're probably working your ass off or life just happens. So no worries ^^
Whatever you feel like doing and whatever keeps you interested and inspired. If you worry too much about what your watchers want to see it can have a really negative effect, i've found. Everyone is motivated differently though. ^^
As others already said. Post what You feel like posting, always eager to see something drom You. And don't worry that much about activity. Lot to do and not enough time, there are important things, but there are things that are even more important.
I think posting sketches as well as full pieces would be fine; post whatever you want to post when you have the time for it. Art takes time, and not everyone has a large amount of time to be able to sit down and work on art. For the longest time after high school and getting settled into a new lifestyle, home, and with starting to work, I was barely active on here for months. But everyone was super supportive of me, understanding, and knew that I would be back at it eventually.
Your art is phenomenal no matter what it is. I'm sure people will be excited to see your work no matter how long it takes, and will stay supportive of you and looking forward to your work showing up, whether it takes some time or not.
I don't work on personal art though... It's only homework and freelance work and I don't want to post that. So it leaves sketches or personal artwork that takes me months to complete and I almost never get to work on it. XD But yeah, I can see a point in that.