1)
In SR5 devices fight back just fine on their own.
All you need to defend yourself is a high firewall and decent intuition/logic/willpower.
Just remember to use matrix full defense and slave your stuff to your high rank commlink or RCC.
Electronic warfare is a great tool to reduce noise which let you remote control your devices over the matrix a lot more efficient.
You need an attack rating if you plan on using matrix combat.
You need a sleaze rating if you plan on hacking and to avoid detection while hacking.
Both are activities that hackers do, not so much riggers.
2)
Sleaze is not needed to hide drones.
They can run silent just fine without a sleaze rating.
(You just roll Logic as a dice pool of it's own)
If nobody is looking for your drone in the first place then you don't even need much logic to avoid detection.
Also, deckers are supposed to be the natural enemy of riggers....
And Drones are hard to spot for magicians using astral perception or projection.....

3)
No that is not legal.
You either slave the drone to your RCC or you buy a cyberdeck and slave your drone to your cyberdeck (or you make the decker the legit matix owner of your drone and have him slave the drone to his cyberdeck).
Only the owner can use Full Matrix Defense.
(and it doesn't matter which device he have his persona when he use full matrix defense or what devices that are slaved and which are not)