on 03.12.2020 07:10
Welcome to the forum,
A quick search reveals a limitation of Windows OS to 2 Tb storage unit. Under windows 10 you can use a native 4k native sector to push the limit to 16 Tb or stay at default 512k sector with 2Tb limit.
Then of course, where is a will there is a way so converting MBR's disk to GPT move the limit to 9,444,732,965 Tb. All this information are available to a quick search on goolgle about "windows disk size limits".
Useless to mention that any change of MBR might end up on reinstalling operating system from scratch.
on 27.12.2020 18:40
Assuming GPT (as sweetpoison mentions), then as big as anything available that fits the Device (SATA/M.2/Etc.) and what your pocket can afford.
2.5" x 100mm x 7mm SATA SSD I think is 8TB (Samsung) at the moment. For M.2 SATA I think it is 2TB and M.2 PCIe NVME 8TB.
One thing you can be sure of is capacities for SSD's increasing dramatically.
Right now I think there is a 100TB SATA SSD available at a price that could buy you a house (depending on where you were of course) and is 3.5". These big boys are targeted at Enterprises.