Well first I think it'd be better to ask you first, what do you plan on using it for? Do you already know what you want to do with it? If not, I would do as others have suggested. Hold back on a rack mounted server for a while, grab a desktop, load it with ram HDDs (or SSDs) put proxmox on it, and tinker with it there. Once you've got that itch to buy more, then now at least you'll know what you need.

My use case is, running some core VMs and LXCs that will run 24/7 along with later down the line some VMs that I'll use for learning Active Directory and performing red and blue team activities on them.

I agree with people on here talking about buying a NUC type box and using that. It's likely to be as powerful or more powerful than the 720, low power usage, basically non existent noise, but you'll be missing out in storage and RAM. The cool part is, let's say you do get a NUC, play with it for a year and then you want to buy more, you can always repurpose the old NUC for some other use. There's also NUCs with dual gigabit/ 2.5 gigabit NICs in them, if you plan ahead for it's repurposing, you could convert it into a very nice router for your network. One WAN and one LAN for your home, then use a switch of some sort to give the rest of your devices connectivity.

But back to what I asked, what do you want to do with the hardware? If you don't have a clue, look at YouTube and search for other people's home lab setups, there's a variety, from purely entertainment like Plex and jellyfin to stream movies across their network, to a security lab for learning AD. Find what you want first, then build what you need for what you want.