An '00 with 27k miles sounds good to me, depending on the price. I know a lot of people with suggest getting an '03, but the changes are worth the extra cost in my opinion. Especially when you can add a glass top to any 986. There's nothing wrong with older Boxster's.
For the warranty a few people have Warranty Direct extended coverage, and it is okay. Sometimes they cover you, other times they don't. I would get a good PPI and see if they have the service records, then shop around for a warranty. Just make sure to read the fine print. I saw one the other day for 6 years/100k miles but the fine print stated they only cover up to $3k per repair.
You don't really have to worry about IMS on pre-'01 Boxsters. It very rarely affects them, except for a few '00 built later in the year. Just check the door sticker for the build date.