?TT upgrade from most basic to next step-up / tube

If you don't want to spend too much more money, I would recommend the Rega line. Even a P2 would be a step up from your Music Hall 2.1 (and yes, I have directly compared both). Better soundstaging and imaging, which if you like classical music and opera, you will definitely appreciate. I have heard great things about the new P3-24, it was not out yet when I bought my P5, which I like very much. I use the Bellari with it, it's a nice match.

The Scout is a good next step up. If you can still get the VPI on sale tables brand new, Music Direct or Audio Advisor has the official lower priced TTs amongst others I assume. You must try it. not a big risk with reslling it if you don't like it. They sell well on the used market. The question is how much will you spend . These were something like $1300 if I recall. No cartridge with that TT. However with a Dynavector cartridge factory installed a few hundred more.The MC cartridge sounds nothing like a MM and you might find it too detailed.Other sonic changes will be very obvious greater dynamics and very little treble roll off.
I know because I own both a MMF-5 Goldring cart and the Scout Dynevector 20X. I think they use a less expensive cartridge now but Dynavector as a rule make good ones.

I had stunning results with a Michell tecnodec as my first table. VERY well built and easy to set up. Sounded sweet. I used and still use a Benz glider H.

You'll get lots of ideas on this but if it were me I'd consider a Scheu Cello the next step up, at around the $1K mark for the TT and then either a Rega or the Scheu Classic arm. Cart could be a Denon 103 if you have a MC phono stage.

If you want to skip that stage and go to the next step after that, the Scheu Premier is what I own at the moment and I am very fond of it.

Your phono stage and preamp questions are good to keep in mind but there is no single right answer. As a general rule on upgrades, I spend as much as I can afford on a single item then save for the next, in this order: turntable, arm, cartridge, phonostage, preamp, amp, speakers. If I've already done the first, I do the second one next, and so forth.

If you can consider the phonostage and preamp separately, buy them separately and spend a bit more on each to get the best possible sound.

As for sonic benefit, the reason many people upgrade is not that they are delighted with their sound. Instead there is usually something they don't like. They then try to improve that point by replacing components with better ones. Once they have got something that satisfies them, they stop upgrading, at least until they hear a much better system.

Try to identify what aspect of your sound you would like to improve. Then look for an opportunity to listen to better systems and see if they have solved that problem.