I need tips when buying a used mustang...

[White GT]

Look like some mods on it. Fox body is good. But not enough stong for old car with mods. It's recommend to add:

Strut tower brace
G-Load and subframe connector to help it a lot.

Code reading and compression test is also necessary.
Code reader for Ford made by equus do the job and it's around 20-30 $ CDN at walmart or Canadian Tire.

Everything else is just about normal driving.

Finally. Two advices about the stangs.

Try to find one or two good local salvage yards. This will help you to save a ton of money on your car when it will break. I hate to pay the retail price for part i can get about for 5 - 10 times less.

The second is about your metro. I don't know about winter in B-C but it's very usefull to have another car. Specially if it's in perfect working condition and if you don't loan money on it too. Often, stang owners are good mechanic. You'll surely work on this car too. Then you'll love to have another car just in case.