As long as you have a safe way yo get the fuel to and from the tank, you are good. I have drilled sending units on Chebbys for a bulkhead fitting and used nylon washers to seal it up, I have used stock return lines, and I have fished 90 degree lines with bulkhead fittings into the fill tube (although that's a pain and sort of hokey)
If you use that vent, you need a vented cap, but the EFI itself doesn't care how it's vented, you just need to have a vent as you use up fuel
What I would do is get it running with the cheapest WHILE SAFE setup you can do, because in the end, you may want to buy a tank or clean yours out well for modification and sink a pump into it. They are quieter by a long shot, cheaper, last longer cooled by fuel, more choices, and cleaner setup. However, you get it safe and running and see if you like it first
I preach this like a broken record, but you'll have to look at your coolant temp and gauge ports. If you don't drill/tap or weld a bung AND you have a heater, you'll need to get creative on gauge and ECT sensor location. As a rule, put the ECT in the gauge hole OR if no heater, in the hole for the heater hose fitting. You need good pre-thermostat water for the ECT.
If you do run a heater, you can put the gauge in the thermostat housing, not the ECT sensor, because it won't be too accurate cold, it is OK for the gauge, especially if you drill the thermostat and can have it spraying there. On installs that I do an intake change, I almost always add a bung so I can run everything, heater, ECT, and stock/aftermarket gauge.