With leaf springs I usually go with the "bolt it on" approach. If they are to soft at first, add an extra spring to stiffen them up.
For height, I always try and make sure the springs have a little bit of arch to them. To much arch and they will be to stiff and give you a really rough ride. A lot of people run with a little bit of negative arch, which gives you more droop, without issue.
I would plan on your axle hight based off of either a neutral spring (aka straight mount to mount), or up/down one inch.