Always get a survey. Always. I'm getting one this week for a steel boat, so I invested a fair bit of energy in finding the rare surveyor who specializes in metal boats.
As for size, the market is very soft (due to aging boomers and "footitis") for small cruisers. You can get completely rehabbed and perfectly good Sharks here in Toronto for $4,000-$5,000 because nobody wants a 24 foot boat, even though they are a near perfect trailerable dry-sailer that is robust enough to race and to sail in the rare instance of 30 knots on the Great Lakes.
If you are looking for a daysailer or a "camping" type experience, and are a beginning sailor, go for older and heavier. In the '70s, I would argue the majority of boats were sold at the 26-27 foot range, and a lot of meticulous first owners are now giving them up, having maintained and updated them for 30 years.
A guy here last year had to drop his 1985 Newport 27 (a C&C hull with a raised deck) to $12K before it sold. The N27 is a decent "weekend" suitable for a couple with enclosed head, galley, six-foot V-berth, etc. It will also take heavy weather, although it's too light to work to weather in moderate seas without pounding.
The point? If your needs are modest, you can get a hell of a lot of good old boat for not much money these days at the under-30 foot level. You can change out the brown plaid upholstery later .