I am using SL1200MK2/4/6 TTables for a long time, love them much for reliability and performance, here is my OP:
1): you will get nice SQ by adding Audio Technica MM cartridge, I personally found the best sounding one is Audio Techinca AT20! Other AT MM carts will work well too, to name a few: AT-150MLX, AT ML160/170, haven’t tried yet latest 740/760 series, but those should be similar. For best results I am using high end AT head-shells, LS/LH/MS series.
2): the best tonearm for SL1200 I tried is SL1200MK4, which is Technics own “audiophile” version of S shaped arms, and uses Titanium to dampen resonances. MK4 TT arm has handy RCA connectors for exploring variety of phono cables. Latest original series SL-1200MK6 table arm is cool too, seems it uses less resonating not fully disclosed alloy, and better wiring, SL-1200MK6 has better main body dampening as well, so, that table is worth to try.
3): There is one improvement I would recommend if you hear inner tracks 60Hz hum noise, is replacing power transformer with better shielded / toroidal one.