I only glanced through the first page of this thread. As far as bar lengths, if you port the 261, it should run great with an 18" bar. 16" is ideal for the 024 and 026, but the 261 was a pretty good bump in performance over the 026. On paper, it's almost as much as an MS361 which is a little overkill on an 18" bar. The reason I say 18" is because you could run that same bar length on both saws. Leave the chain on the 261 set up like stock with the drag links at .025", but drop the rakers on the 462 to .040 and let it eat. 18" will be long enough to handle over 75% of your needs and it will keep the weight of the saw down. It's also nice to have as many common components as possible between your saws, especially the consumable ones. Rock an 18" chain out on the 462, just grab another out of the tool box, or grab the B&C off the 261 and keep going and full speed. Rock a 25" or 28" chain and that saw will be out of operation for the remainder of the day. I have my 036 set up this way with a 9 pin rim, and it's a real pleasure to cut with. With a sharp RSC chain, it eats through oak, hickory, and locust like nobody's business. I'd say like a hot knife through butter, but I really don't think that a hot knife would go through that much butter that fast. Especially useful when I'm cutting medium to large limbs off flush with the trunk. The extra power makes a huge difference cutting through what is essentially one big knot. The 462 would just take it up another step.
I'd also recommend getting at least one bigger bar for the 462 to start out with. My 064 normally wears a 28" bar with .404 chain and pulls it very well. Works great on large rounds over 24". 28" is also a great length for noodling large rounds into smaller pieces that can be lifted onto a splitter. Its long enough that even on 24" long rounds, the nose stays clear of the wood on the other side (burying the nose eats a lot more horse power/torque), but it's not so long that it sticks out too far and risks getting into the dirt.
As far as oils and such, I run Stihl's 2 cycle mix exclusively. Other's may be as good or better, but we've been running it since the early 70s and have never had an issue. My main gas can is 2 gal. I buy the bottles for 2.5 gal and mix it a little rich. I do that partially because I always end up overfilling the 2 gal can with gas (Rec 90, non-ethanol from the pump), and partially because I don't really care if the saw smokes a bit or the plug gets fowled a litter faster. Plugs are cheap, cylinders are not.
I run the cheapest bar oil I can find. If I'm pushing the limits of what my saw can do as far as providing enough oil (like having a 42" on my 064), I'll grab a bottle of Stihl and just grit my teeth and eat the cost. In the dead of winter, I keep a bottle of Stihl's blue bar oil (their winter bar oil is in a blue bottle) handy to mix in with the cheap stuff. That stuff is as thin as water, but it will flow decent even when the temps are in the single digits or below. I use an empty bottle of Tide to pour out of because it drains back into the bottle, and because the bottle is orange and easy to see in the woods. If I need to mix in the thin stuff, I just add a little to the Tide bottle, and move on.
Eventually you will probably end up with a bar longer than 28" for the occasional really big tree. I would think that the 462 could run up to a 36" bar which could easily take down trees in the 6' to 7' range. If you run into a tree bigger than that, it's worth buying, renting, or borrowing a bigger saw for a day to make those cuts. There are plenty of 066/660s around (as well as other brands), and those saws need an opportunity to stretch their legs once in a while
