1. Assuming it's structurally sound, nothing wrong with the FN as a basis and it sounds like you'll have a nice pair of rifles.
2. How patient are you? Splitting up the work sounds like a guaranteed way to make the project take a long time, but if you are particular about who does each piece of the work, pick and choose who you want to do each part of the work. One thing to consider, if you aren't happy with the end result, who do you go after to redress your issues? Personally I'd go with one reputable timely smith, pay what he asks and wait patiently.
3. I've never dedicated the funds for such a project so can't give a personal recommendation. I have used discount smiths in the past and have been unhappy, so would do the research on what smiths are considered top of their game. You could look at ACGM smiths.
4. Integral is a slick way to go, but I've had soldered on bands and sight bases with no problems. A money personal preference thing, I see either route perfectly acceptable.
5. If you're happy with them, stick with them.
