Firewall/NAT

It's been almost a week and I'm going to start losing hair I think.  I've used monowall for my old connection that was like this for years and loved it:
IPs 65.x.x.2-6
GW 65.x.x.1

Now we've got a new internet connection that's like this and I just can't wrap my head around it at all.
Company IP: 65.x.x.90
Gateway: 65.x.x.89

Usable IPs: 65.x.x.202-206
Gateway: 65.x.x.201
Mask: 255.255.255.248


Is this the right idea for the setup I need?
1. WAN
Company IP: 65.x.x.90
Gateway: 65.x.x.89

2. LAN
192.168.1.0/24

3. OPT
66.x.x.200 / 29

4. Proxy Arp on WAN
66.x.x.202-206

5. Some set of NAT/FW rules?  Is Advanced Outbound NAT required?
Can I NAT stuff to 65.x.x.90 at all? Or is that IP off limits and I can just do stuff with the 66.x.x.202-206 IPs?


After poring over google and monowall docs for the last week to limited results, I consulted my ISP which is telling me I need to shell out a wad of cash for a Cisco 2600 and can put my Monowall behind that.  Maybe I do, but I hope you folks can tell me what (most likely simple) thing I'm missing.

Thanks in advance!