5 colors should be just fine; no reason to have a super big heavy reel that has 10 colors; especially for walleye. I just do 3 colors on a lot of my rods. A few other things:
1. Leadcore will give a different action to lures (especially spoons); always good to have it in your arsenal. Sometimes it will outfish the other rods, sometimes not.
2. I typically like running leadcore straight off the back (no boards), one long rod on each side of the boat, and then run deep diving cranks off mono on the boards.
3. Suffix Advanced leadcore I really would recommend.
4. Leadcore is very speed dependent; going faster or slower will greatly change your depth.
5. When you’re factoring in depth, typically add how much the lure would go down without leadcore. For example, I use suffix advanced leadcore that goes down 7 ft per color. For example, a #7 shadrap will troll about 10 ft down unassisted. If I have 2 colors of lead, my depth is approximately now 10 + 2(7) = 24ft. And yes, to answer your question, 2 colors of lead mean 2 colors totally submerged in the water.
6. You’re not supposed to attach lead directly to a planer board, although I have done so here and there without any line breaks or anything.