Checl out our review of the Wesena HTPC-e5 chassis. It sounds like it may be just what you are looking for. There are a ton of other options out there other than Antec. Wesena also has larger chassis in the e6 and e7.
SSD for OS is recommended if there is money in your budget as it will bring more of a CE experience.
As far as external vs. internal storage, people will use both depending on what the goal is. I’ve gone from having an SSD and 4 HDD to an SSD and 1 HDD for recording with all of my archived storage on a WHS 2011 box.
