does it have quick change barrels?
not yet, L6 has states that he plans to work on that in the future, but in my opinion realistically, you don't need one. Red Right Hand is making barrel/gas tube heatsinks which seem like an interesting idea. I think it's possible, and would be cool, but just really extra for something that is supposed to be a cheap AR15 compatible belt fed.
Any specific SS you are using? I am considering a Disruptor FRT for mine but on the fence.
What do you consider the hardest thing with the DIY build?
Will be using a Arc Fire, currently just have a regular SS with a Geissele trigger.
All lever style FRTs will be better due to the mechanical advantage the lever provides, I don't know about the Disruptor but Rarebreed/traditional FRTs can cause bolt drag when you pull the trigger as the bolt returns. just do the ARC fire if you want a traditional selector, it's easily the best.
This autistic guy even sells precut RAVE triggers that work with the ARC or regular SS.
As far as "difficult" parts of the build there were three things.
1. Barrel drilling: at the end of the day, this is janky no matter how you do it. The instructional video shows L6 using a hand drill with like a 5/64" bit to start the new gas tube, IMO it's almost impossible to not snap a bit without using a drill press. but like in the original post, the KAK barrels they sell are a pretty good deal and unless you want to do something silly, it's not worth it, I think KAK also has SBR sized barrels and 300BBC ones if you want to go that route.
2. you need to bend a return spring, it's what holds the "feed lever" in place (part No:3, L6 version is solid and a different color)

Bending isn't hard, but the instructions are lacking and basically, "use plyers to make this weird shape, shove it in here, and make sure the feed lever moves, but doesn't move "too slow".
I really think you could make a jig for it, and that would make the instructions much less ethereal.
3. there are a few very tiny set screws that if you fuck up, can basically ruin the entire build, So I'll include just general stress about either loosing one of those or stripping one of those. or for one, red loctiting it (which is needed because it's near the barrel nut) and letting it set in the wrong place, bricking your upper. It's just a little stressful. I had a non critical threaded hole not threaded properly, but as mentioned L6 quickly provided the proper threading and I had a tap n die set that had the bit I needed, I was a little stressed snapping the tap there but it came out OK.
But as mentioned, the build process isn't too bad if you want to go that route, especially if you've done different "difficult" builds before.