Advise before joining the AM family

Hi, I live southern California and in the early stages of purchasing a pre-owned 2005 or 2006 DB7 (V8 preferably). This is going to be strictly a weekend car so Im expecting to put less then 3-5k miles on it per year. Ive come across a few DB7s that caught my eye with 25K to 30K miles on them already. Now some of these cars don’t have all their service records and some have records of work done by independent specialists.

1. how important is it that the work was don’t by an AM dealership?

2. what is the Aston recommended service schedule? Since Im buying a used AM, Im wondering what things I should make sure have been serviced on the car (Oil change / major tune up / Timing belt / Clutch etc etc)

3. What can I expect when/if I take a 4 year old AM with 30,000 miles in for routine service?

Thanks
-Kia