Andover offer a variant of this bolt/plug, with a magnet. I'm going to fit this to replace the original one since it's a little bit mangled, and will be checking it at the next oil change to see what will have happened in my oil tank.
As for the oil filter, provided you or the previous owner/mechanic didn't over-tighten it, a strap wrench like this is all you need to remove it:
Always inspect the new filter for any foreign particles, swarf, damaged o-ring, etc. Here's the new filter:
Motobatt unit. I've not tried these before but they're popular, fairly cheap and maintenance-free. I also tidied up the battery tray and it looks considerably better than the unholy mess I had there before.
Here's a neat tip: use a wide strip of aluminium tape to secure extra fuses to the battery: