“the idea is to get a future proof turntable”
I hate to say it but SL1200 is not something I would consider a future proof TT. If you want to dip your toes into record playback, go ahead with SL1200. If you’re the type that prefer the best then you need to budget around $5K. Alternatively, look for used bargains on TT’s.
A good analog setup requires serious commitment and $$$$.
My reference for start up cartridge is Hana ML MC Cartridge - $1200. Your built-in Marantz phono EQ would suffice for now but eventually you may end up upgrading to a better phono. When I started with analog few years back, I was pleasantly surprised by modestly priced Parasound ZPhonoXRM - $249. It was so easy to use and sounded incredibly good with a $3K TT and Hana ML Cart.
Basic products for cleanup….depends on whether you’re digging records through bargain bins at local thrift stores or buying new records 😊
Be patient and soak in all the advise coming your way from some of the experienced members here and then plan your purchase.