On long trips: I did a two week trip in my Catalina 25. I found that to be a bit too long, but I think that an annual week long trip would be fine for a couple. You'll want to be careful with how you pack, there isn't a ton of storage room. The best storage on the boat is keeping stuff in the quarterberth (which is huge) while sleeping in the v-berth.
You do get standing room (around 6'6") in the main cabin with the pop-top up. You'll want to make sure that you get a boat that includes the pop-top cover, they are expensive and hard to source apart from the boat. You don't get it over the galley area, which is a bit annoying.
It is a big step above camping.
The 25 is a much better boat to own on a budget than the 30, and likely than a 27. Any Catalina 30 that is in the same price range as a 25 is going to have a nearly 40 year old inboard engine. Replacing the inboard (which will be almost inevitable) will cost you $10-$15k. 27s came in either configuration (inboard and outboard), but if you get one with an outboard you want the model designed for it, not the inboard model with an outboard added on. The transom is different on the two boats, and the outboard model has a semi-well for the outboard that brings it closer to the centerline by over a foot.
Sail size is related to displacement, and the 27 (50% heavier) and 30 (over 100% heavier) will take much more expensive sails. To put this into dollar context a sail for a 30' boat costs about twice as much ($1000 vs $2000 ballpark) as one for a 25' boat. Good sails make a huge difference in boat performance and comfort (old sails overpower the boat and cause it to heel more).
Now you bring up another question. Why do old sails over power the boat? My wife does not like it to heel to much