I'll address #2, the hardware platform:
I disagree with the fellow who had "issues" with SMP Intel systems. I have been running dual processor linux machines for several years (in production environments). If you pick decent motherboards, and use recent kernels, you'll be just fine. Stock RH 6.2 comes with an SMP-friendly kernel.
The boards I've had extensive experience with are:
Supermicro P6DBE (BX board)
Supermicro P6DGS (GX board)
Intel 810EAL (i810 board)
I've been using these in production environments under Linux, NT4, and Win2K Server with current uptimes in the hundreds of days. For SMP machines, I like the GX board a little better since it has an integrated dual channel SCSI controller (Adaptec 789X) and supports 2GB of SDRAM.
Avoid Intel 820/840 boards like the plague unless you are going to spring for RDRAM. I took the plunge a few months ago and had *major* problems with *every* 820/840 board tested with SDRAM. They are ALL extremely unstable.
You'll also want to spring for a nice hardware RAID card like the Mylex ExtremeRAID 1100. I'm using one of these with 9 18gig Seagate Cheetahs in RAID 5 mode. It's not as fast as software RAID, but it seems to be less fragile. The drivers for this card are mature and it is the speed king for hardware RAID on Linux these days.
Those comments are directed at the database machine. For the web servers, you can just buy a pile of the 1RU boxes from rackmount.com (my favourite), penguin computing, etc. and load balance them behind an appliance like a Cisco LocalDirector or Foundry ServerIron (my favourite...it's cheaper and faster). Load the machines up with as much memory as they'll hold so they cache everything and consider a cheap IDE software RAID0 of 2 disks for the disk subsystem. It's cheap, and it's "reliable enough" and "fast enough" if you have a stack of them load balanced. If you lose a disk, your only real important data on that box is the webserver and security logs since the last backup. If that's a major trauma, use RAID1 and take the performance hit. These can be had for about $2k each.
Here's my current setup. I've been VERY happy and it has scaled VERY well. I'm not using ACS in production yet or postgres, but I'm planning on "repurposing" this gear for that soon.
Database box:
Supermicro P6DBE
2 x PIII 850mhz (coppermine) w/256k cache each
1GB ECC SDRAM
Mylex ExtremeRAID 1100 card
9 x 18gig Seagate Cheetahs in external enclosure (using 3 separate SCSI channels on Mylex card...3 on each...one disk is designated a hot spare)
Intel 100BT ether card
Matrox G200 video card
some cheap Toshiba ATAPI CDROM
some cheap TEAC floppy drive
stuffed in 4RU case for computer and 4RU case for disks (bought cases with lots of fans from rackmount.com)
The above machine has been up since early April and I haven't even needed to login to it. Rock solid.
Web Servers (using 5 at the moment):
Intel 810EAL motherboard (integrated 100BT ether, audio and video)
PIII 733 processor (133mhz bus)
512mb non-ECC SDRAM
cheap Quantum 20.5gig 7200RPM IDE drive
(going to being doing software RAID0 with 2 of these soon to improve speed of reads when cache misses and writes of logfiles)
integrated 3.5" floopy & 32X CD-ROM (nice for 1U boxen)
1RU case with 2 "hot swappable" drive trays
These are all sitting behind a Foundry ServerIron load balancing appliance and have not been rebooted since early April. Again, rock solid.
I've never had more than 400-500 simultaneous users, but even then the machines were not anywhere close to capacity. A planned upgrade for the near future is to add a 2nd database machine and switch to Oracle (so I can do useful synchronization for some level of fault tolerance on the RDBMS side).
Hope this helped.
Cheers,
