If you already have the hardware, do a test fit and see how it goes. I don’t have any rgb ram so I have no idea how tall it is. All my sentry systems are using ultra low profile ddr3 so I had fewer issues than some with fancy, taller ddr4. Custom cables aren’t 100% necessary but if you have the budget for it, it really cleans things up and can remove clutter. Maneuvering custom, individually sleeved cables is also easier though iirc the platinum corsair psu comes with individually sleeved cables? So you may have better luck with stock cables. The gold has stiff ribbons, so custom cables were a godsend for me.
Also I have no experience with the 5700 or 5700xt, only a handful of people over at Hardforum.com have used them in Sentry afaik. Again, if you already have everything, see how it goes. Worst case scenario you can undervolt or lower power target.