When we backflush we're cleaning all the parts of the brew path in our espresso machine that come into contact with coffee. Perhaps most importantly, we're cleaning the brew valve.

Coffee will leave a little bit of itself behind on everything it touches, so regular cleaning is required to prevent buildup. Oily, sludgy deposits inside your brew valve can restrict movement of the brew valve plunger, impede flow through its orifices and compromise seals. When pressure is released at the end of every shot, coffee has an opportunity to head "upstream" from the puck, through the brew valve and down the drain. Backflushing helps keep all this clean by forcing cleaning solution through the same path.

When you backflush with detergent, you're mixing up a little bit of cleaning solution in the blind basket at the group and then sending that solution back through the brew valve and down the drain when pressure is released.

I always recommend focusing on the grind before the dose.  On this type of grinder, whenever you adjust the grind it will affect the dose.  You'll generally get less output for a set time the finer you go.

Best practice is to keep the dose consistent by weighing and manually adjusting (scooping out a bit with a spoon/adding a bit by tapping the manual grind button) as you're dialing in the grind. Once you're happy with the grind setting, then tweak the set time to get the desired dose.

Apparently, quite a few.

A solid preventative maintenance plan.  

Yes.