Do you think my 8GB Pi 4 can handle ElectrumX + Bitcoin Core?
I was trying to set up ElectrumX on a 4 GB Raspberry Pi 4 and I gave up after a week. The initial sync was taking too much time and I ended up building a normal server (the sync took almost 3 days on an SSD and a recent Intel i5 CPU). If you are patient enough and have some solid cooling system then sure.
I don't have any patience for a Raspberry Pi to do anything remotely taxing. Even a heatsink kit and fan don't seem to help a lot, but setting up the Pi to boot from a fast USB 3.0 SSD will help some. Once everything is synchronized it might be fine for a node and ElectrumX, but I've never had a Pi run trouble free for long-term with any remotely taxing tasks.
There are ways to find cheap PCs with i5 processors for about the same price or less than a Raspberry Pi, and realistically they're way more practical for your expectations.