Suggestion for a five star hotel env

Hi guys, after a long time...

I have to make a pbx system for a 5 star hotel in my country, cox's bazar in bangladesh. I'll heve around 400 extensions (i assumed it as a max number of ext). 280 ext are room ext and some are official ext (around 20 I hope, thus 400 is the max and more than max...).

There will be at least 10-15 PSTN connectivity so 10-15 PSTN --> 400 ext. May be i may need to restrict some ext to deny the pstn dial. I'll need to allow all room ext for pstn and also most of the exts to dial pstn. so there will be a lot of simultanious channels (say for 15 pstn trunk, 15+another 15 = 30 at least). Fax is not required here. I want to use the TDMoE converter from SpiderMUX. All most every sets will be traditional TDM sets. and specially all of the rooms will get those leagacy sets, not IP sets... So I need some guidlines on the whole project. Like the hardware, cards( is there any way to avoid cards if I can use SpiderMUX??) Also for load balancing, I can include multiple boxes of trixbox but that need IAX to be config and also billing is a very important thing for me. Thus I want to keep it simple like one box for room exts, and another for office use.. (best if all in the same box).. guys, please advice....