I'm a little confused about something.

Firstly, is it possible to allocate the same IP to WAN and LAN interfaces of
m0n0wall?

At present, my IP config is the following:
192.168.0.1 - m0n0wall LAN interface
192.168.0.3 - my laptop
192.168.0.4 - my desktop
192.168.254.253 - m0n0wall WAN interface
192.168.254.254 - router

The subnet is 255.255.255.0 (or /24) in all cases.

What I'd like to do is allocate a range of IPs in the 192.168.0.x range to
both subnets, rather than having 2.

So something like this would be ideal:
192.168.0.1 - m0n0 WAN
192.168.0.2 - router
192.168.0.4 - m0n0 LAN
192.168.0.5 - desktop
192.168.0.6 - laptop

I understand I'd need to change the subnet, and that I could have
192.168.0.0 - 192.168.0.7 as one network and 192.168.0.8 - 192.168.0.15 as
another.

But can I split the subnets up further, so that I can have 8 IPs in the
first network and just 2 in the next?

Or do they have to be in equal blocks?

If any of this makes sense!!