Custom Rear Motor Mount Insert... https://www.amazon.com/dp/B00MDVPFLS?ref=ppx_pop_mob_ap_share
Best bang for your buck first mod. You will need to shave down the part that goes into the mount to get it to fit though. I used a dremel with a sanding wheel and just kept removing material and then seeing if it would fit. You want it to go in as tight as possible. You'll notice a direct improvement in power being put down to the road. Caveat is you will feel some more vibration in your steering wheel over the super soft stock ones. I think it's a fair trade off for the price.
Thanks! I had a 16 veloster so I know a lot of parts are swappable. I assumed the suspension was the same but you guinea pigged that for me. Here's one of the first mods I did that I was certain was the same part https://www.amazon.com/dp/B00MDVPFLS?ref=ppx_pop_mob_ap_share
One of the best bang for your buck mods out there. Real, noticeable differences for $40. You do need to trim the bottom of the mounts down a little to get them to fit in the bracket. A Dremel and ten minutes accomplishes that.
Easy stuff like intake to get started. Maybe shift cable bushings or intercooler resonator delete. Something like this if you want a little more grip and don't mind a little but rougher idle https://www.amazon.com/dp/B00MDVPFLS?ref=ppx_pop_mob_ap_share