Please do. To summarize: 1. N900 stock kernel does not have module support for nf_conntrack et co so just building the modules is not going to help, one needs to flash a kernel that has support for inserting said modules.
3. Current efforts with "custom" (basically stock kernel with just the modules required for NAT) kernels lead to reboots with more than light traffic, likely due to device watchdog tripping. (Except maybe Jebba but AFAIUnderstood his kernels are more customized)
5. There has been a vague report of managing to do NAT in userland, however there are no details and while I have a vague idea of how it might have worked I have no idea how to actually implement such scheme. being able to do this in userland would circumvent the watchdog and requiring kernel flash problems.
6. Infrastructure mode hasn't been investigated yet properly, trying to set the interface to infrastructure mode via iwconfig fails but it's even not supposed to work, no-one has reported any experiments regarding hostapd. OTOH Ad-Hoc should be more than enough (and in some cases possibly better).
8. Rumour of the "real JoikuSpot" for N900 has been mentioned (if it is real it will be interesting to see how they tackle the modules issue) That should cover the essentials of the thread so far.