hello again, and "Northern" phonemes

Been a few months since I've had time to post to this list (or even read it
much), but hello again!  Hopefully I'll have a bit of time for conlanging
over the next little while....

I'd like to ask people's opinions on how plausible the following phoneme
inventory is.  It's intended for a people in my book whose culture is still
very much under development (I'm just calling it "Northern" for now, until
I know enough for a better name).  The inventory is somewhat eccentric
(well, linguolabials alone do that), but I hope doesn't go too far:

(in CXS)

consonants:
p  t_N t ts) tS) tK) k q  ?
p\ T_N T s   S   K        h
m  n_N n               N\
B                L

short vowels:
i     u
    @
&     Q

long vowels:
i:    u:
    @:
&:    Q:

diphthongs:
i@    u@

&@

Opinions?

Ian