Weighted keys are of course a good idea for a piano player and work well for a lot of instruments, but I would also really recommend to look into MPE - it’s one of the big revolutions in electronic music production and enables you to play expressively like with a string or wind instrument. So instead of velocity and aftertouch you have 5 parameters for every key or finger and can control every aspect of a sound, be it a violin, a panflute or a new synth patch you just made… A lot of MPE controllers are pad-based in one form or another, but there are new controllers coming out all the time. Some have piano layout (like the Seaboard or the one by KMI), some more non-traditional (my fav the LinnStrument is more like a guitar). Really really cool stuff. It costs a bit, but there are some relatively cheap options. Here is some more info on the topic:
These days most DAWs come with good effects that cover the most common basics and do the job. For some more exotic effects (something like Zynaptiq Morph that does spectral morphing between two sound sources or complicated playable auto-glitch and -modulation effects such as StutterEdit for instance), or for a certain specific sound or specific options (Pro-Q does dynamic EQing beside constant EQing, Pro-R has frequency curves for decay time and so on), or for workflow and UI preferences, it can make sense to buy additional VST effects, but you can do A LOT with DAW effects. Additionally, DAW effects often use less resources as some of the VST options out there.
With VSTis, the story can be very different imho since 1) synths are usually more complicated and therefore leave more room for differences and unique aspects 2) you often spend more time with synths when building sounds, therefore GUI and workflow differences are more important and 3) if you are using a lot of presets instead of or additionally to making your own synth sounds, getting multiple synths just for the different (sometimes extremely huge) factory soundbanks can make sense.