It isn't clear what "hitting so much" means.

First, the system will run better with the 8G module removed, leaving only the 32G.  That way, 32 G RAM will run at full bandwidth.  With 8+32, only 16 G RAM of your total is running at full bandwidth.  The rest is running at  half bandwidth.

Second, if the issue is slow performance in games or under heavy load, has the system been thoroughly cleaned internally, with replacement of the thermal pads?  It's around 3 years old, meaning it's overdue if it hasn't had internal maintenance.

If you need more storage, by all means upgrade the SSD -- and yes, 2T will work.  The new SSD will not run any faster than the original as the system is old enough that its interface is PCIe 3X4 -- not the PCIe 4X4 that newer drives are capable of.