For the Maxhaust it is not really plug and play, You actually have to dismantle some connectors and split them open, you need a good eyesight LOL, they are small and tricky to open.
In fact you insert a new module which has a normal clipping connection socket, 2 CAN bus wires from the original module have to be disconnected and reconnected to the new loom to the module, they supply all the bits, but it is quite fiddly.
Before 2016 it is in the boot, after it is under the driver's seat, boot is MUCH easier.
Yes for the 1st part, I have never had the forced regen, so I can't comment on it. I've never had the count down on the dash.
There is also a sort of self regen, without injecting extra fuel, it is like self cleaning when you're driving at good speed (revs) on the Mway and the temperature in the DPF is sufficient to sort of "self" burn the soot.
This system only works on the latest cars where the DPF is right after the turbo for High Temp, and not under the car like in the past.
There is also the EOLYS system but that's for Peugeot's it drops the burning temp. of the soot, but has for inconvenient to clog the DPF on a long run!!