Tyres are the only thing that keeps you on the black stuff
The make, age and size effects grip, steering feel, noise and comfort
Depending what's already on it can make a difference
A car of these age often have, either very old tyres that have gone rock hard or mismatched tyres of budget brands, cracks, bulges, bald, nails, incorrect pressure and sometimes even the wrong tyre have been fitted
One of the first things when you get a secondhand car is to evaluate the tyres, you may strike it lucky and it's got new premium tyres fitted,all round it would be silly to not use to there fullest first, there is a date code on the tyre, by 7 years they will be well past there best, regardless of wear
I put the deepest tread at the back, it's counter intuitive as the backs wear slower, but when the fronts wear out and you fit two new tyres the rears then became the fronts and you constantly replace only two tyres at a time, and using each tyre to its full, with the added bonus the car is less likely to swap ends in standing water, if the car is little used this will not work, I find 3mm a good place to start thinking about replacing a tyre, yes I know the legal is 1.6mm
Personally I look at noise, price, economy, wet weather grip of the tyres in the size I am looking at, you priorities might be differently
I also don't buy tyre that channel the water into the centre or directional tyres except for snow tyres.
It's getting harder to do deals with garages over the last few years, but it's always worth asking for a price individually first then ask if there's any discount if you order two or four,
