My advise:
Have your axle completely ready to go before you start cutting off your ifs, in order to minimize downtime on your rig.
You could take your frame jigs and tubes somewhere and cut the holes in the frame and center them and weld them.
I have seen guys weld on their front hangar before they cut their ifs off, but i wouldn't recommend it. I like to see the shackle angle before i fully weld the front hangar on.
I didn't have a plasma when i did mine, and i rented a welder.
I used a sawzall, and an angle grinder to cut my ifs off.
It wasn't horrible, but did take some time.
Paying a shop to do it sounds really expensive, if you have the skills to do it then you should, well i think so anyways.