1) What does a drone roll for defense against attacks? Normally it's Rea + Int, and drones use their Pilot rating in place of mental attributes, but I don't see anything about what would substitute for Reaction. My best guess would be that they roll Pilot x2, but I can't find anywhere that actually states that. Also, a driver or jumped-in rigger uses their normal Rea + Int for the vehicle, correct? Meaning a rigger isn't any better on defense than a manual driver?
2) Do drones have the option of using non-sensor targeting? It looks like they do (the example on p.184 compares a drone using sensor targeting vs. not) and the -3 dice for sensor-based attacks against most targets means it will usually be the better choice, but I'm not sure what that would represent.
3) Are drone-mounted weapons limited to a single clip/magazine/cylinder of ammo? Weapon mounts can hold lots of ammo, but it doesn't look like we have any rules yet to modify weapons for belt feed.
4) When can you get the benefits of a smartlink with a drone weapon? Actually, it looks like I answered this myself while searching through the rules -- the description of the smart firing platform (p.433) says you can use an implanted smartlink when remotely firing a gun in VR. So it looks like using AR with goggles that include a smartlink won't work.
5) This isn't quite drone combat, but what's the limit on programs that can be running at once on an RCC? Equal to device rating like cyberdecks? Do they take up Sharing rating as if they were vehicle autosofts?