Absolutely no pearls of wisdom here - I'm picking this up as I go along.
Absolutely nothing adventurous here as I'm a mere beginner.
First job for any new bike with unknown provenance is oil and filters.
Warmed the engine up and tried to budge the drain plug. No joy. Needed a breaker bar on it and seriously thought i was going to pull the whole sump off, but it did eventually give and (only) 1 litre of warm black treacle came out. The magnetic drain plug looked like it had a spiky hair cut it had so much swarf on it.
This is not a good start.
The oil filter housing produced another half litre of oil, and the next suprise...the wrong filter !
Here's what came out, and what I put back in :

Looks like the filter may have just been covering the bottom oil pickup hole but barely - so hopefully some filtering has happened.
Looks like the previous owner wasn't too hot on maintenance.

Filled it up with 3.5 litres of good stuff. I'll do the oil and filter again in 500 miles and see where we are...