You would only really need one port or one nic in a pfsense box for each customer. If they ran >1 machine then you'd just need a hub/switch to connect each of their machines back to that master port/vlan.
Still, if I get 20 customers with 2 rigs, I'd need 20 ports. That's going to either be extremely costly on a pfsense box (with NICs that have four ports each), or would require some special router. I would rather go the router route to begin with, but I have no idea what I should be looking for as far as features go.
You're going to be hard pressed to offer space for the prices your mentioned. Don't forget fire suppression, multiple ISPs, UPS/Generator and redundant power feeds.
Without the ISPs you're a DDoS away from losing customers.
Without a UPS/Power conditioner one lightning strike could do you in.
Multiple power feeds are also a concern along with standby power. How long is acceptable downtime?
There's a reason most CoLo facilities charge $150-$200 base + a charge per extra 1U per month.
The point of this would be to offer low-cost CoLo for miners. It wouldn't have all the features that your typical datacenter might have, and probably won't have the 99.% uptime that your typical datacenter might have.
- Fire suppression is important, but I would only go so far as the fire marshall/insurance required on that front.
- I wouldn't have a UPS/Line conditioner or generator. People could provide their own if they like. The most I will provide is a fuse-protected power strip.
- There wouldn't be multiple power feeds. We VERY rarely get any sort of power outages here, so I'm not worried about that. In the city, we probably get 1 power outage every two years.
- DDOS is a major concern, and something I am still researching (and open to suggestions on). I have several potential providers, but am unsure that any of them could provide DDOS prevention in any capacity.