What a lovely first quilt! I also think the simple geometrics with straight lines are a good quilting choice - SITD or diagonal would both do very well. I think I would choose a yellow thread that blends with the yellow squares. The glorious thing about quilting batiks is how forgiving they are so even if your straight lines (or whatever motif you choose) are not perfect the batiks will camouflage them. Post more pictures when you are finished!
Alison