Homebrew PCBs

I'm attempting to create a fairly sensitive sensor system and I'm 
getting cold feet about the PCB design. I've come up with a few 
different PCB layouts keeping in mind decoupling digital chips, 
trace lengths, yadda yadda yadda, to keep down noise and noise 
sensitivity. Thing is, I don't really know if what I'm doing is any 
good.

Does anyone know of a design company that can take a schematic and 
do a good double sided though-hole PCB layout from it? Preferrably 
one that'll email me and say "Are you sure you really want to do X, 
or hey, you forgot Y...

Enclosures also seem pretty hokey - is there a company that will 
make small runs of enclosures, say 10 or so at a time?

Yes, this may well end up a commercial product so I'm not expecting 
to see "free" and bargain hunter specials.