Hey Richard, welcome to the forum!
I don’t recommend steel strings on any of my kits and I’ll explain why. Each part of the kit is selected to work together. Nylon strings are easy to tie to the leather tailpiece and easy to keep in tune with the friction pegs. If you use steel strings you’ll almost definitely need to find a tailpiece that will work since the strings won’t have a good way to attach and can stretch the leather.
Then you may need to upgrade to machine tuners which I didn’t really design these kits for. You’ll see that on the friction pegs you wind the string downward and close to the peghead, you can’t do this with most machine tuners and the string will sit higher on the post, causing less downward tension at the nut and possible string buzzing issues.
Another point to note is that these necks do not have truss rods so they could become distorted or twist with higher tension strings, though I wouldn’t really be too concerned with this as they are pretty sturdy necks regardless. The last point: the drum is a tackhead which means it’s only as tight as you make it the first go, and can’t be adjusted to compensate for higher string tensions at the bridge- in short the skin could start to sag from extra tension.
I chose all the parts to work together in harmony, so changing one small thing could mean you must change several other things to stay in balance.
These are my recommendations and reasonings, but you are free to experiment and try out anything you want because it is your banjo and the main point of these kits is to have a fun hands-on project.