yes that system would work but be rather costly as your gettingsome parts you don't even need in that size like the 2.5" hdd much better price/capacity if you step up an inch.
psu would work although you would have to buy the DC version of the mobo as sometimes they are built in sometimes you need the extra £25 add on cards to convert the power.
memory any memory stick would work from any company don't just buy from mini-itx.com - news
they are very expensive for what you get, hence why I put them as an (info) link not as a reccomended place to buy.
I would buy from Kustom PC's
email them the parts you want and they will source them for you and they answer your email within 30 mins of receiving it they really do care about there customers.....
most people go with cubit cases or nexus as they have interchangeable colours and plenty of room...
Kustom PCs Hoojum Cubit 3 White
you do seem to be goingfor true smalle3st of the small cases which are normally classed as car pcs