It's all a matter of preference. Try what you think you will like, but be prepared to make some changes along the way. I have 2 planted tanks, 1 with driftwood and 1 with a big (plastic) rock that I attached some plants to.
There are a lot of threads showing pics of planted tanks. Browse through them and see what suits you.
As far as putting larger plants in the back, thats the way many people do it. However, if you want a more 'natural' look, try mixing them up a little but be aware that you may block the shorter plants from view if they are behind something that grows full and lush.