Technics SL 1200 GR

Also, what's the difference between the 103 and 103R? Latter is a $150 bucks more. 

I’ve never heard the AT so unfortunately I can’t give a good comparison. I know there are reviewers out there who swear by the Denon 103 and review carts costing 4K+. 
 

I looked up your amp. It appears to have a MM and MC setting only. There doesn’t appear to be any resistance loading options. When it comes to MM vs MC Lo, the physical install complexity is the same, but electronically they are very different. A MM cart puts out about 4mv, and required about 45db gain to get it up to line level. A MC Lo puts out about .3 mv and requires a SUT or about 65db gain to get it to the same level.
 

assume (assume being the key word) that your amp’s MC input is preset to about 60db gain and maybe 100 or 400 ohms resistance. There is a formula used for determining the appropriate resistance for an MC cart. The 103R has .25mv output and 14ohms impedance. The 103 has .3mv output and 40 ohms impedance. The formula is to determine the step up ratio required (5mv / cart output mv), square that value, and divide it into 47,000 ohms. This gives you the natural impedance of the input. The cart wants to see 10 times it’s internal impedenece. For the 103R, this means a 1:20 step up ratio and about 117ohms natural loading - and the cart wants to see something above 140. That’s about right. For the 103, this is a 1:15 step up and about 177 ohms natural input loading - but the cart wants to see more than 400 - that’s not normal. Normally, if your above the resistance, you’re OK. If your below, the cart gets ‘pinched’. 
 

What does all this mean? The 103 is an OG cart and best uses if you have control over the resistance. The 103R has more normal specs and is probably more forgiving. Reviewers tend to say the 103R provides more ‘high end sparkle’ - if that’s what your looking for. 
 

Needless to say - this is complicated. It’s more complicated than what o have here because the 103 is an unusual cart with a lot of history and folks who tweak the load to suite their tastes. Ideally you could find out what the load is on the MC input of the amp and let that be your guide. Better yet, someone else has heard both and can make a recommendation. 

As far as a weight gauge, it’s used to set the tracking force. With the Techniques, they will tell you to mount the cart and zero out the counter weight when the arm floats above that table. Then, based on what the cart manufacturer recommended for down pressure, adjust the counter weight. The stylus gauge lets you confirm this number by taking an actual reading instead of using the marks on the counter weight. I have never found the table to be off by more than a 10th of a gram- so really not needed unless you end up with several carts and head shells and need to switch them out often. I have one brace I listen to a lot of mono and 78’s - so 5 carts for me in rotation depending on the albums. 

@zazouswing haha, that went right over my ignorant head. I guess I'll stick to the AT cart for now and revisit the Denon and other MC carts a few months down the road.  I hope the AT won't be too disappointing, esp given that I haven't heard that many turntables sing. Its been a 100% digital until now. Excited and nervous at the same time. 

And it helps to know that I don't need a weight gauge at this point. Thanks again!

Go with the Least Expensive model TT of a High End TT Mfgr. like EAT or Michell. You get a better made TT than the upper end tables of a mfgr. that makes $400 TT's.