Wow, Fox bought a new car
Regarding the wheels, personally I think they look good, but if you want to change them you could just wait until the new tyres are worn out and then replace the wheels at the same time? (How long will this take roughly?)
Also what are you going to actually do with the E39? I totally get why you want to keep it, but I'm curious as to what you'll use it for, and what you'll use the F10 for, and when these usage patterns may cross over.
It's a shame you're keeping it, I'd have been tempted to make an offer haha.
It's a really easy job, unless you're allergic to spanners. It'll be a case of setting aside a Saturday morning, dismantling any bits in the way (vac hoses, cables/connectors etc) and unbolting the rocker cover. Fitting is reverse of removal making sure you use any gasket sealant where required, and torquing the nuts up in the right order.