You're going to have a little tougher time finding a 5-space, unless you find one on eBay or some other site for used gear that someone had specially made. I'd say go for a 6, so you'll have a little more flexibility if you want to add/remove any gear, and you'll have an easier time finding a case. Next, what level of protection do you want?
Try looking
here to get an idea of the different levels of protection/weight/price/etc.