Some time ago i have made a decision about making budget loop and it was worth it. Go for CPU only loop and later you can always expand to GPU also. Just get proper size radiator. When you will get the watercooling components they will stay with you. Pump, radiator, fans, fittings etc are parts that you don't have to change every time you swap pc parts. Olny GPU block is tricky because its hard to get core only GPU block now (i've used mine for 3 cards, GTX 580, 660 ti and 970). Or you can get fullcover and sell it later, and get some money back. What you get on return is the silence and cooling capacity. All that is out of the reach of any air cooler and aio is not expandable and also not as good as custom loop. Hope that helps.
Ryzen 5 3600 | ASUS TUF B450 PRO | 2x16 GOODRAM IRDM PRO 3600Mhz DDR4 | MSI VENTUS GTX 1660 Ti | PNY 1TB NVMe SSD | IN WIN 303 | be quiet! STRAIGHT POWER 10 500W