1. Are you using stock rear leafs? If you are then you will need to add a few more leafs to handle the weight.
2. I don't know about the highsteer hitting the front leafs (who told you this?). I am using rear springs and have plenty of clearance. My pitman arm does hit my springs a little at full compression, but thats nothing to worry about.
3. For the rear hangers just go with a front sas hanger. Not the whole thing, just the spring mounts.
4. steering shafts- I broke the two plastic pins holding mine together. It will extend a long ways. Then we just left it and it doesn't move in or out.
5.I don't have any experience with a TRD locker but i wouldn't think it would matter.
Hopefully any of this will help.