More memory is always good, but I would try to get an i5 prior to go more than 8 gbs of memory.
The way I think upgrades for general use (non gaming or anything need a graphic card).
Haswell Pentium First with 8gb->Decent SSD like at least 128 or a 256 of tier 1 brand->I3->I5->16gb->better ssd like a 480.
After that you can't really improve it much, you can do marginal improvements but the key word marginal. Now some things such as video rendering/encoding would prefer an i7 quad core to an i7 eight core (damn that is sexy saying that i7 eight core with 16 threads, repeat after me SEXY) but for most usage models you will not go above 4 cores at 3.7 ghz.
Now I would highly recommend a good monitor, something ips/pls and at least 1080p but preferably 1440p. You can get Koreans for roughly $300 and brands such as ASUS for $500. Now 4k is awesome but I would wait a little longer for the price to drop for nice panels and not tn stuff and for the various OSes to get better resolution support. (why is not possible in windows for the software to think I am running a 1080 panel if its not dpi aware and and a 4k panel if its aware with a checkbox under preferences for each individual program. I would gladly lose the 1 pixel and just do a 2x2 pixel doubling or the graphic card smoothing out the colors so you get the best of both worlds.)