You cant game much on that laptop since it only has integrated intel Graphics and you cant update them. But SSD is always very fast and future proof since you can move it to new laptop aswell. Looking from crucial your laptop supports sata3 which is fastest you can have. So first you should get brand like samsung evo ssd 120gb is a good size if your not keeping much stuff other than few games and files at a time.
i3 is a dual core so no matter which generation it is... dual core can even be problem watching 1080p videos so getting i5 or i7 would be nice option. Important, download prime95 and hwmonitor. Run hwmonitor so you see cpu core temperatures and then run prime95 on blend default settings for 15-30 minutes. What core temperatures you get about? Maximum?
Your HM75 chipset supports up to i7 but your motherboard bios could of locked cpu support to only i3 or i5, so its kinda risky
Check TDP should be 35w and there is i5 and i7 models which have that, if you go over 35w there could be problems like thermal heating and you would need new heatsink, that could be the case even with same tdp i7 but less likely.
Intel Core i7-3632QM would be best 35w TDP it has 4 cores and 8 threads running at 2.2ghz i have no idea about price.