Where would the Airstream be located? One spot where it's warm? Traveling? Those are also considerations.
Also, $2500-3000 budget for renovations but what would you be starting with? That's not a huge amount of money so you'll need a trailer that is pretty much in working order, not a true "fixer upper."
That said, we have a 25' Airstream with a family of three. Thus far our longest trip has been just over two weeks and the Airstream was more than fine - we had plenty of space and plenty of extra space. As a point of reference, we ate two meals outside of the Airstream on that trip, so we use the trailer facilities a lot. And we weren't always hooked up to water/power.
We have talked about possibly full timing in 2017 but for now it's just a discussion. If we did, we would look to purchase a larger trailer so we can:
1. Add a larger kitchen.
2. Create two "bedrooms," one of which would convert to an office space in the daytime (for me to work and for our daughter to home school).
3. Add a washer/dryer. This isn't so much to wash clothes but really for drying. On the east coast we have found that towels and things just don't dry. Even a small dryer would help make full timing more enjoyable. There are combination units that probably could be retrofitted into a trailer (SOB's have them).
If you are looking for inspiration and ideas, I like Travel Trailer Renovations by Hofmann Architecture
. They have great modern feels to their renovations. But yes, they have higher budgets.