One thing you won't need is a gigabit switch to run the Obis, they will run quite perfectly in a standard 10/100 switch as the Obi runs at 10. If you're going to have more than four items plugged into your router, just plug the switch into your router. If you need a switch, I'd opt for an 8 way.
You do realise you have 4 voip lines in a 202.
Most voip numbers are 2 channel, meaning they will handle 2 simultaneous calls. Some suppliers like MyDivert sometimes provide more and you can point the number to your voip account if you don't use them (MyDivert) for your service.
If you're going to use IP phones, you don't need the Obi's, just get an IP phone that can register 4 voip accounts. You can get 4 line cordless IP phones but they can be pricey.
As far as I'm aware, it doesn't matter how many calls are using your IVR, the limiting factor being the channels on your DID.
For fax capability, if it's just for inbound, use a fax to email service - saves a lot of paper, if you intend to foip (fax over ip) then choose a voip provider who supports this - not all do otherwise you could fax over your landline. Alternatively, there are quite a few free email to fax providers on the internet and if you rent a number from them, you get inbound and outbound faxing using email. Probably more reliable than trying to foip.
