A few comments from me:
Yes, use 32bit - the type of processing load that LMCE typically suffers does not lend itself to 64 CPUs ie you really will not get any noticable performance improvement from 64 bit, but you will possibly experience some of the downside instability issues. Its a no-brainer.
You are not using Windows now - simply don't even worry about RAM. A simple core can get away with 512M if you are that way inclined. I would recommend 1-2GB. 1GB is sufficient even for reasonably complex setups, I would challenge anyone to prove they have a setup so large they actually need 3GB!
On the 3GB question, this is a common misunderstanding. Windows can handle a mapped address space of 2GB for a process
(unless you use the /3GB switch). It is similar for Linux (both 32bit). But note, this is per process. When a process is context switched in, it can own this entire address space. All other processes' pages are not mapped. So there is nothing stopping you having more than 3GB physical RAM, its just one individual process cannot use more than 3GB in its virtual working set. There isn't any process on this system that comes anywhere close to that! As long as you have enough physical RAM so that the total working requirements of all processes are reasonably satisfied to minimise (hard) paging, you are fine.
I have seen nothing in your posts that explains why you cannot use DHCP for everything. Again, this is a no-brainer - on the one side, LMCE depends heavily on its modified DHCP to provide pnp and device re-detection services (among many other functions), and on the other side there is no disadvantage to using LMCE's DHCP.....
Remember (this is true for most DHCP, but particularly for LMCE's) - once an IP address lease has been handed out by LMCE's DHCP server, that device will stay on that address indefinitely. Another common misconception is that DHCP IP addresses (in this configuration) change ... even infrequently... They do not! Even if you were completely to rebuild your LMCE core - it would still hand out the same IP address to your Windows_PC_1. If you were then completely to rebuild your Windows_PC_1, it would STILL get the exact same address!!! The only circumstances where it will loose the same address are 1) if you were to leave Windows_PC_1 off for a long time (>1week) and another, new device comes onto the network after that time and by bad luck gets that address; or 2) if you were to rebuild both your core and Windows_PC_1 at EXACTLY the same time as each other; or 3) if you change the NIC on Windows_PC_1 and then rebuild it....
ie unlikely. Take a look at this .... http://wiki.linuxmce.org/index.php/Network_Setup