Can I create a 4TB Raid 1+0 volume?

Every filesystem has limits, and ext2/ext3 were limited to 2 TiB, but ext4 has a much higher limit (that you won't reach anytime soon). So, use ext4 and you should be safe...

For NFS shares I think it depends on the NFS daemon/version you use (check the manuals first) and some certainly have a filesize limit. For Samba it shouldn't be a problem, except with older versions of Windows maybe?

All this sounds like it should work fine.

You can use Software RAID to create the Raid 10 partition if your hardware doesn't do Hardware RAID.

The only issue that you might face is that /boot can only exist within a Software RAID 1, so if you are using Software RIAD you may well need to create a seperate /boot partition outside of the RAID. If you are using hardware obviously this is redundant.

The size limits for partitions are imposed by the filesystem itself and if you are using ext4 (the default for Ubuntu) the size limit ofr partitions is 1 Exbibyte so you should be fine ;)

You may have some driver - issues, but I've found my way around them. I figured I'd be ok purchasing an EVGA motherboard -- still had issues with the ICH10R. But I've found that this community is very helpful in troubleshooting issues if & when they arise.