you dont have to convert anything.
if you leave the t case you have in your truck right as the crawl box then you can utilize the forward shift. If you are scared the new case might leak then you would have to buy a conversion kit to do so, or swap around the shift rails from case to case. You only need a top shift in the rear case because you will have no where for the forward shift shifter, or shift rail for that matter, to go.
If that doesnt make sense let me know.
As for all of your other questions which weren't really answered,
you want to push your front axle as far forwards as you can if not you'll regret it down the road. I would use the trail gear hanger I have it on mine its super low pro and actually moves the axle forwards the most if you mount it right. Its also not a big drop hanger. When installing it you should move it forwards from sitting flush on the frame. Halladay said look at his, I did his solid axle swap we moved the skys hanger like a 1/4 forwards maybe more like 1/2 not sure off the top of my head but with that and his mixed pack of rears his axles about 3 or more inches forwards.
When you do the rears I would use boomerang shackles because they are meant for a steep shackle angle without making contact with your body mount so no notching required.
When you do the rears and everything then you must use high steer and an Ifs box as well.
