ok, so I was surprised to find that I own 8 right now, if you include basses. I'm not including my non-guitar/bass instruments or it would be well into the 9-12 or higher category.
electric guitars:
Northern Les Paul (vintage, mid 70s, made in japan, history tells me it was made by same folks making many of the Agile japanese guitars of the day.... INCREDIBLE guitar, easily the best LP I've ever played, and it's beautiful too)
Line 6 variax 300 with sperzel locking tuners, graphite nut. cool, fun, dozens of very believable guitars in one, and a nice feeling guitar to boot with great natural tone of it's own... modded with a custom made single coil pickup in the middle position as well for that LP junior sort of thing. edit: I should add that what I mean is I added a switch and a pickup, these have none stock, I wanted to use it as a regular guitar also though so did this mod for reliability among other things.
Ibanez RG-370dx with the wacky multicolored finish - completely trashed when it fell off the back of a moving truck at high speed and it's hardshell case blew up leaving the guitar sliding down the highway FACE DOWN... hence I bought it from the previous owner for a few bucks in functional but very damaged condition. I'm still working on the cosmetics of this thing cuz it's just nasty looking, but it plays amazingly and I've done the following to it: Evo I in bridge, fernandes
sustainor in neck, ibanez in middle (quite a decent pickup actually), modded tone control and capacitor switcher for two different resonance points (only affects the bridge and middle pups, the neck is a buffered pup). really incredible guitar - my low budget DIY flo
I'm certain I have another electric but can't think of it now, maybe I don't? hmmmm
EDIT: just remembered, so it's actually 9:
my lap steel electric. dumb me, forgot I have it at all. forget the brand, chinese, but fantastic sounding single coil 6 string lap. like it better than a vintage fender I played recently that lacked any life to it's tone.
acoustic guitars:
applause ovation shallow body - damn if I don't just love this guitar to bits. sounds/plays like a much more expensive shallow body american ovation I played, just incredible, and easy to play for me since I can't handle high action thick strings on acoustic
cheapo nylon string acoustic I picked up used as trade for a $30 dano distortion pedal. guitar's nicer than the pedal LoL... I wanted nylon for the occasional recording session and it sounds just fine, plays alright too actually for such a cheapo guitar.
BASSES:
Sunny 8 string (non-octave) fretted with custom made single coil pickups with wood covers, custom active electronics. nice bass - like galviston (which are cheap 8 strings) but with the custom pups and electronics sounds absolutely amazing. got it for $200 cuz it had literally useless pups and was unplayable (several notes actually misfretted to the wrong notes and buzzing and high action all at once LoL). with extensive setup and fretwork and DIY new pups an electronics it's become a semi-pro level instrument, and it's as pretty to look at as to play and listen to.
Cort 4 string fretted - gb-54 - a really nice bass with zero resale value cuz it's made in indonesia, great built in preamp, great pups that just needed a subtle change in resonant frequency (lowered a bit) to give it more bite and presence, all done with $3 of parts and some know how. my main recording bass now. incredible low action, really a player's bass. got it for $100. yea, you get the idea, I'm cheap, especially for a pro.
chinese bass, rebranded as MRW, that I defretted myself - got it used for $60 with an amp LoL, in mint condition, needed huge setup work before fretless conversion so imagine how much work it needed after LoL. needed a shim in neck after. but wow, great sounding fretless, nice dual humbuckers with all passive electronics, also did some resonance frequency tweaking in electronics (I don't know why this isn't done more often... it's the easiest way to alter the tone of your pickups).
So that's 8. yea, not all collector's items (only one is actually and even then not an "obvious" one), but all are great player's instruments and I use them for paid session gigs all the time.
other instruments are:
5 string banjo of decent prosumer quality (kind of old too)
small vintage german mandolin
acoustic violin (which is a priceless Amati from more than 300 years ago)
acoustic viola (belongs to my buddy but have had it for 15 years now)
electric violin (chinese, sexy looking, tweaked like crazy, modded electronics and setup, autographed by my favorite current musician Devin Townsend)
roland drum kit (I don't actually own an acoustic kit right now but use an amazing milestone kit for tracking at my regular studio - roland is basically triggers that I swap for better samples at mix time, great for producing my own drum parts, nothing like really playing for inspiration and feel....)
yamaha sy-22 synth
korg digital piano (weighted, 88 key, used as midi controller mostly and for rehearsing with stock sounds)
roland mc-505 groovebox/synth/drum machine/sequencer
then it's the estoeric and world stuff.... pan pipes, chinese uhrtu (sorry dunno how to spell these things), lap kalimba from africa, some hand drums and percussion instruments (I have been a percussionist and drummer on albums even though I try to focus on other instruments), and then it just gets into the weird stuff that I won't bother mentioning.
so... guitars (including basses)? 9
if you include banjos and mandolins, 11.
if you included other string instruments (violins/violas, uhrhu), 14.