Looking to upgrade

Old Build New Build Just a couple questions

I already have a crucial p5 plus for new pc, should i replace my sn750 until i’m able to build my new pc since i only have 1 m.2 slot?

Wondering what you guys think about whether to keep gpu for awhile(40 series looks kinda overpriced imo but would prefer to stay nvidia for software features)

air cooling vs. aio vs. custom loop

If i go custom loop, soft line vs hard line

and other overall insights Thanks in advance!