Hello Gunslinger! I reread this thread from the beginning and thought I’d give you my take on some of the issues you’ve raised. Keep in mind these are my opinions; they are reasonably well informed, but not the last word by any means.

1) Oil: I think you are wise in choosing a synthetic oil, and 20w-50 is the correct viscosity. You’ll find many who will insist that synthetic oil should not be used in older cars like the Mini, but I’ve never heard a reasonable explanation as to why. Usually, the rationale for using a non-synthetic is  “older engines were built using more primitive alloys and larger tolerances and therefore were designed to use the oil available at the time.” Until I see more convincing information, I'm not buying it.

Additives and heat dissipation notwithstanding, the primary purpose of engine oil is lubrication, and synthetic oil is way slipperier than conventional oil. A couple of caveats; our engines require a zinc additive. If the oil of your choice doesn’t contain zinc, zinc additives are readily available [link]. Caveat no. 2, because our engines share the oil with the transmission, synthetic oil is so slippery that the balk rings (synchros) in the transmission don’t get a good enough bite, and the gears will occasionally crunch during a shift, unless you do a good job of rev-matching. Some synthetics do a better job than others, synchro-wise, so you might want to experiment with different brands. I did, and finally settled on an oil that allows the synchros to do their job reasonably well. 

2) Grill removal: You’ll be surprised at how often you’ll need to remove the grill. Get a set of “Grill Buttons” [link]. I also replaced the sheet metal screws that fasten the upper part of the grill with riv-nuts. Much easer [link].

3) Nosiness: Well placed DynaMat (floor pan, backside of firewall, doors, etc.) will reduce interior noise by 20-30% [link]. Headphones and/or ear plugs will take care of the rest [link].

4) Radiator hoses: I’d replace all of your black, rubber water hoses with silicon [link]. There’s a huge range of quality when it comes to automotive rubber. I wouldn’t risk it. Silicon hoses last a lifetime, plus they look great. Too flashy(?)—get black ones.

Anytime you have a gathering of gearheads there’ll be a wide range of experience and knowledge. This forum is no exception. Some members can assemble a motor with their eyes shut, while others have never changed a spark plug. Most of us fall somewhere in between. The trick is figuring out who’s who. Fortunately, most of the newbies here tend to have more questions than advice, and the experts have a degree of modesty and humility—rare for experts in any field. You’ll figure it out. Good luck!