Speeds over 1gbps are still costly. Not like it used to be but still a cost driver. If you increase your amount to 350 you could use a 4mb 64gb like this
Slap opnsense or pfsense on it and you’re good to go - like this dude did
I’m no routeros guy but I don’t trust mixing default and tagged packets. I do believe on UniFi stuff you can mix as default is tagged 1 on trunk ports. I’d just make a vlan for each network. Raw internet, IoT and LAN