I guess "officially"  we're talking about the first car you bought yourself, so in your case it would be the Mustang. Interesting, my second car was also a '64-1/2 Mustang coupe which I bought for $50 after the Impala was wrecked. 289 factory 4-speed with rotten rear frame rails, which my uncle fixed by cutting them out and welding in new steel. Really fun car to drive.
What engine/tranny did your Mustang have? Was it a coupe or fastback?

Just the fact that you still have it is impressive let alone your list of mods! Judging from all the suspension upgrades it sounds like you're setting her up for the track... do you plan to do a little vintage road racing when she's finished or would you rather not risk 'bruising' her?

No worries, as far as I'm concerned everyone should do whatever they like to their cars without worrying about what anyone else thinks. I like both original and modified cars, and I understand the 'classic look, modern performance' philosophy completely.

Looking forward to some pics when she's done.

I am so lucky I still have my first car 1964 galaxie conv.  I bought it when I was 12 for $1000.00.  My parents told me they would not buy me a car so  I saved every penny I could and saw the car 1 mile from my house . It had an OK body horrible black interior and and good running 1973 302 with a 2bbl. My parents made a deal every dollar I put in they would match.  I loved cars but knew nothing (hell still don't know all that much).  I ripped out the interior and fiberglass the holes in the floor board ( I know but I had no clue how to weld or have the money to do it right) The fiberglass is still holding after nearly 30 years!.  I drove it down the street a few times sitting on milk crates.  Just before I turned 16 got some body work done and a respray and new interior and top, still have the receipt was only $1495. Could not afford original style interior so it was pretty basic but its hanging in there and mainly white seat covers are sooo much better in Florida.  I am biased but I thought it was the coolest car in high school.
sounded good looked good, but not too fast to kill me. 

3 months after my 16th birthday I blew the master cylinder and had to pump it to get it stopped and keep pumping it to keep it stopped.  Took it to local brake place and mechanic crashed it into concrete ditch  he panicked, caught the gas pedal when brakes went to the floor.... Best thing that could ever happen,  It wasn't totaled but very close.  Got all new front end and full professional respray of the whole car.  new radiator(old one was leaking) new rebuilt transmission as the the housing was broken (old one was starting to slip on 2-3 upshift) new water pump and got FORD on the hood (was missing two letters)  

Drove it through High School and actual once to college for a semester Florida to Ohio and back no problems other than blocked heater core on way back (big jacket till got in south GA).  It then sat barely used for three years.  It has only left me stranded 2x, fuel pump and failure of axle bearing.  I lost freeze plugs, drove it home put in those rubber expandable ones that have been in for 25 years! just turn the nut a little when they start weeping. I have rebuilt power steering control valve and new hoses, rebuilt the carb put in a new distributor with pertonix ( I never could get points perfect) rebuilt brakes new flexible lines. and had to have the flywheel replaced after the teeth ring separated from rest of the flywheel and new heater core.  It also had some suspension work done, upper inner shafts, but I didn't do that work. That is pretty much it, pretty amazing and lucky on car I have had for almost 30 years.  I keep thinking one day I will walk outside and it will literally fall apart  like the car in Blues Brothers.  I keep saying I will take it off the road and restore it right but it just wont break and I love driving it on errands and on the weekends.  I have two kids and I let them sit in my lap and tool around the neighborhood.  I am very lucky and thankful.  

My first car was a 1958 Chev that I purchased for a buck. This was my girlfriends aunts car that had been sitting in a field for years. I towed it home, did all the required maintenance added a battery, bled the brakes and away she went! It's funny, I was told by my girlfriend at the time that it was a 2 door 57 Chev..when I got there it was a pink 1958 four door Chevy..still a cool car nonetheless. Cheers!