Age old discussion I know but MM or MC? Benefits?

Oh yes, it is much better to overfill with the oil than underfill. One bottle is good for five times, I think. It is recommended to change the oil once a year if you play it a lot and every 18 months if you don't. Besides getting small metal particles in it, oil gets consumed, burnt.

I don't know about the Shelter cartridge, but with my Goldring MM it took me some patience to set the anti-skate right. It was slightly better in one position with some music and slightly better in another with other music, but these were very small steps.  With VTA set by ear I ended up with the arm in parallel but you have very different and heavier cartridge.
Yeah, Larry should be able to assist you in dialing it in if you need it.

Great. Yes, the Shelter is liked by many with Nottinghams. If you have questions regarding the set-up you might want to talk to Larry from Hollywood Sound, he knows Nottinghams and I think the only distributor/dealer in the US. He also likes MC cartridges. You will probably want to use original Nottingham oil that he should have, though you could get it cheaper from the UK dealers. Belt lasts a long time but still you may want a new one. And of course you will need a record mat to replace the stock. Most people prefer Boston Audio graphite mat, but the company is no more so it's difficult to find. I am sure you read the Nottingham threads on Audiogon, see what alternatives are there. Also, as I remember, just about everyone used one of the three isolation platforms under Spacedecks - 2"-3" maple block, Symposium or Neuance (no longer made) but you can start with the platform it comes with. I use 3" maple block with Boston Audio tuneblocks under it.

Uberwaltz, you really have to have Nottingham Spacedeck ! Or at least Interspace deck. I wouldn't have it if it didn't rock, believe you me. But I listen to acoustic music, Spain's flamenco, world music, vocal in addition to jazzrock and some rock. So I need a very versatile cartridge. Sure, $2500 Tranfiguration Axia or maybe $1600 Lyra Delos would probably do most if not all things better than my humble 1042. But I really see no need, not to mention the cost, until I upgrade my Acoustech phono. And since I want good tube phono it will be at least $2000. So, a lot of money.
Of course, you could try Dynavector 20 LO, many like this cartridge. If it works in your arm. Perhaps you would like to take a risk with something used bought from a reputable member, just to aquaint yourself with MCs.

I read that Soundsmith cartridges must be very precisely aligned, with VTF and anti-skate equally precisely set, that’s that they are more capricious than average. But this might only be true in some not all cases.

To have both is an excellent idea, either with one table or two. But that's not the option the OP is considering. Again, table rocks cartridge follows, well, if it does.

Don't know about these particular arm and phono but Grado can be an excellent rock cartridge, or Goldring 1042 or one step down. I use the 1042 with Nottingham, speed and resolution are good for MM and it rocks. I listen to jazzrock among other things.

Simple. For rock you don't need MC cartridge. What you need is a great turntable. Upgrade it if you can. You also need great amps. You might want to upgrade your cartridge to another MM later. Well, you could try $1600 Lyra Delos if you must but why ?