Baxi Multiheat

I bought a house a two months ago and it is heated by a Baxi Multiheat woodpellet burner. I think it's about 7 years old. It heats the water, underfloor and sometimes a few radiators. I had it serviced as soon as I could, and I keep it running constantly as advised by the chap who serviced it. I have no experience with them at all, and zero plumbing/heating knowledge. To be completely honest I'm a bit intimidated by the Baxi.

A couple of questions...

When I took out the ashes for the last two weeks I noticed a substantial crust of black sooty stuff at the bottom of the opening where the auger is visible in the back of the combustion chamber. I took the crust out each time. I was a bit worried that this might be evidence of back-burning or something. Is it normal?

How often do I need to clean the boiler thoroughly? (Taking off the side panels, etc, not just removing ashes.)

There have been a couple of power cuts here over recent weeks. They got me thinking... what happens if the power goes and the auger can't move pellets forward? Will the fire just go out or could it cause problems?

I fill the hopper from a silo using a bucket. I seem to be really getting through the pellets. How many average-sized buckets should I get through in a week?

I appreciate the time anybody might take to answer my questions. I'd love to be able to maintain and manage the Baxi myself eventually, it's just a question of getting my head around a few things first.