I’m not sure of your exact question. In general, Domino on Linux will work very well.
Your hardware looks good to support the user count. My only concern is whether the drives are SCSI or SATA. I would definitely look to SCSI as the performance really makes a difference on higher user loads.
I would look at either Domino 6.0.5 or if you can go straight to 6.5.4. ScanMail 3.0 for Domino works very well so you should be good there. I’d skip the Norton Antivirus for Domino product as it no where as good as ScanMail. If the server is a dedicated Domino server, you shouldn’t need any other AV software for the box than ScanMail 3.0. BE 9.1 should work great.
You didn’t define whether you were planning to run RedHat or SUSE. Lotus seems to be favoring SUSE these days (look at R7) but either will be a good choice. Given my druthers, I’d start with SUSE if possible.
Hope this helps. I’d be happy to help if you need further information.
Ostly Consulting Group