Usually the service prices are defined at local level and so you will get a more accurate estimate if you contact the garage you want to use. Just make sure that they include everything that is advised by the manufacturer.
The MPG will be down to you. I have seen a high mileage third generation on Auto Trader with an avarage 83MPG photographed.
As you are buying used, use the number plate to compare prices to website like the
http://www.blackcircles.com/ You will find from cheap value tyres to expensive performance tyres and anything in between, including winter and all seasons tyres. It all depends on the result you want to achieve and how much you are willing to pay for it.
The used car stock will vary a lot depending on what has been put on the market. If you are looking for a specific version only, you may have to wait longer.
The leasing companies can make deals to buy the car from them. So you could investigate the option of buying the 3 if you like it.