Just ordered this one today for work:
http://www.qnap.com/pro_detail_feature.asp?p_id=192
Think it was about $230 AUD with no HDD's which is pretty good. Looks like it would fulfil a lot of your requirements. I was actually reading about it getting a bit moist thinking I could do with one of those!!
We also have a TS-209 at work which we have had for ages, runs sweet etc.
If you wanted four bays then look at the TS-412.. but I dunno of the price sorry.
Pretty sure most / all NAS's are admin via a web browser so you can use whatever (IE iPad if you want)
Keiths a funny cunt aint he?

This one time me and Keith mooned a train full of old ladies

Think they quite enjoyed it myself.