Hi elementalwindx,
Figure that most of the folks here use FreeNAS as a simple front-end to one or more ZFS pools. ZFS works best if it has direct control over the physical disks, consequently most of use use plain old dumb HBA's and let ZFS do both the volume management & the file systems. With a proper hardware RAID card you usually have to do something like make each drive it's own RAID-0 volume and present the whole mess to FreeNAS, honestly about all that does is lock you into needing to use another (similar) RAID card if yours fails.
For battery backup you would use a stand-alone UPS, the way you would with any system you care about. FreeNAS has support for a number of different makes\models, use one that's supported and FreeNAS can shut the box down if the power outage outlasts the batteries.
Honestly using 8 SSD's for your pool is most likely a waste if you are just using gig-e. Most of your performance will be lost as soon as you hit the network. If you are looking to reduce latency you are still going to have to deal with all the latency inherent to going through the network to reach your storage.
As to your questions in the original post:
Intel NICs are the safe\go-to brand for all things network-related in FreeNAS\FreeBSD. You should check the FreeBSD HCL for 8.2\8.3 (depending on which version you are running) to see if your prefered controller is supported. Odds are, if you are using LSI the controller will be supported, but with FreeBSD it is usually wise to not use the latest & greatest cards as it takes a while for new device support to make it into FreeBSD. FreeNAS is currently running on FreeBSD 8.2 which is one release in the 8.X series behind. You could try the 8.3 beta & see if you have better luck.
One thing you can do with FreeNAS\ZFS is use SSD's as read & write cache. In some cases the addition of these devices can result in dramatic performance increases.
I strongly recommend you take a look at this guide:
http://forums.freenas.org/showthread.php?t=7775
that one of the users put together.
-Will