New to forum and Vinyl

Sorry, yogi, but switching it off does not bypass all of the extraneous additional circuity in the built-in USB/phono stage. Heck, just the mention of a "switch" tells you there is some amount of unnecessary circuitry that you might want to eliminate. BTW, this is not my finding. I read it in some of the review comment sections.....

Now, whether or not it is audible in any one's particular system is another story.

I agree with reubent and would stay away from the AT LP120USB. I have read more than one account that bypassing the built-in phono stage results in unacceptable noise levels. Many owners are removing it altogether. This is but one of a bunch of problems with this TT. I have read accounts of loose tonearm bearings, high w&f, and actually seen one where the black paint was flaking off the platter strobe dots. Never seen this on a Technics.

Suggestions on a TT/cartridge/needle in that price range would be great. I really like the manual turntables

Since you said you are comfortable bringing a vintage TT up to speed yourself, you are wise to consider a manual TT only. Far less to go wrong as there are no automatics and inevitable degreasing to deal with.
Consider a good used Technics SL-1500 or SL-1800, servo controlled direct drive TT. They are very easy to work on and are strictly manuals. About the most they would need to a good deoxidizing of the speed pots and possibly refilling of damping fluid for the cueing control. Plenty of online videos and instructions showing you how. They have fully adjustable tonearms, anti-skate and removable headshells. You should find these units on your local Craigslist for around $150 but they will still require the above despite what the seller says, And you can't go wrong with a good SL-1200 MKII or its later incarnations.  There are many out there that just seen home use so try and avoid one that was used for DJ'ing.  If you see an Ortofon Concorde or cheap Shure at the end of its tonearm, run from it.  It was probably a DJ table.

Speaking of Craigslist, I strongly recommend buying vintage on CL only as you will be able to inspect the TT and possibly audition it too. You can’t do this on Ebay and most selling over there have no idea what they have nor are they able to properly package it and ship it.

There are many manuals built by Pioneer, Kenwood and Marantz from that era too. Find a good Micro Seiki from the late 70’s like a DD35 or DD40 and you have found what was considered high end back in the day.

Whatever you buy, don’t put stock in the cartridge as that is pushing 40 years old and should be replaced or at the very least, stylus replaced. So I would worry about the cartridge after you have found a good quality TT.

First, have some fun. Loved the older Marantz gear and owned much of it. For the TT, I'd suggest checking out the U-Turn stuff. I just ordered their top end player w/ walnut plinth and am quite happy. Good choice if manual works for you. Secondly, I feel for little investment you can better those speakers. I remember them from my 70's heyday reading Stereo Review etc. Ultimately, that's where the music comes from. To me, used TT's are a real crap shoot. If there is one delicate component in the chain, that is it. Good luck and enjoy the ride.

Rega has been a good value for many years

Best value: put the turntable & its pre-preamp in a different room as close to the main system as possible (so you won't need long wire runs)

drill some holes in the wall if you need to...

Why would you do that ?