Looking at your current specs your build does look nice.
Things to keep in mind (from my experience) -
1. Future-proofing requires you to think about your workloads in the future as well.
2. RGB is good for aesthetics but a bit heavy on the pockets. A normal 16GB 3600 MHz Ripjaws kit goes for around 7.5k in Online. As far as I know a RGB kit goes for around 9.5k.
3. Air coolers are on par to liquid coolers if you select the right one. Only difference is noise (if you run fans in your room don't consider this), case size, aesthetics and price. The one you have is a decent cooler but it's a budget option and you can save 2.5K by getting a budget Dual tower Air Cooler for 5k (ARCTIC Freezer 50) or a high end one for around 7.5k ().
4. If you choose to go for an AIO Liquid Cooler make sure the fans that come with the case are matching the ones on the AIO else your aesthetics will suffer.
5. If you are planning for a Gen4 SSD, it won't affect your daily workloads until and unless you are a super busy content creator whose time will get wasted in editing by 10-20 mins. If your aim is future proofing, getting a Gen4 SSD isn't beneficial as current scenarios indicate that reaching those levels of data transfers will take time. Saving money here will help you get more storage. For 15k you can easily get 1TB gen3 SSD with a 1TB HDD/500GB SSD (and have some money left over for a OS SSD of 120GB if you chose to go for a budget Gen3 SSD).
6. You can use your saved money to get a better Case, SSD, Fans, an RGB light strip or even Games. Alternatively you will have around 5-7k left to invest in a better GPU.
All these are suggestions based on your starting post stating that you are going for a budget PC. Remember that saving money in one area can let use it in other areas and that some components like storage and fans can be upgraded in the future. At the end of the day it's your PC and you should decide what PC makes you happy irrespective of how much you have to spend over your budget.
