Turntable newbie info site?

I know I may have rushed it, but reading about all the improved musicality of TT, I just bought on Audiogon, a like new Technics SL 1200G so it will work on my McIntosh MX 135 pre-amp which I understand has a MM phono stage.  

It is being delivered next week so I would like recommendations on a MM "starter" or more intermediate cartridge that would pair well with my new to me TT.  I listen to classic rock mostly with some classical as well.  

Any Grado would be a good match with the tone arm on the Technics!
https://www.needledoctor.com/analog/Phono-Cartridges/brand/Grado-Labs

Congratulations!  There is a huge difference as everyone says here with Digital sources.  You've skipped in my opinion the starter steps in what you've bought.  I am very inexperienced compared with all the guys here so I hope I'm not wrong here but as regards cartridge, I believe it's an even bigger influence on your sound.  MC vs MM ?    MM is perceived as lower end because the theory says that a coil is lighter than a magnet so can respond quicker to the bumps and troughs in your groove.   High Output Moving Coil cartridges can also be used into MM inputs although models are more limited.  Dynavector and Sumiko are examples amongst many.  You've a few days to read all the reviews.  Needledoctor is great source but read the descriptions because High Output MC cartridges are on a page labelled Low Output!   However, like all things its not black and white, MM can also be better than MC.  

Nice! Welcome to the Technics club.
If you want something special look for vintage MM like the Audio-Technica AT-ML150 (Beryllium cantilever, MicroLine diamond) or Victor X-1IIe (Titanium cantilever and Elliptical tip). Both are excellent cartridges for reasonable price, more expensive than some modern Nagaoka, Grado and usual suspects, but with obvious advantages over them all (different cantilevers and diamonds). On exotic side you can look at the ADC TRX-2 (Sapphire cantilever, Vital II diamond). Anyway, depends on your budget, some Stanton/Pickering top models are also superb, and don’t gorget the Grace top models.

Agreed, you're already in the best community and resource already. Technics 1200 is a great entry. Many people dream of owning one. I have technics 1210 in my collection with these sorbo isolation feet,  https://mnpctech.com/pc-computer-stereo-desktop-case-feet/technics-turntable-replacement-custom-feet/sorbothane-audiophile-turntable-vibration-isolation-dampening-feet.html