The 25' is a great size unit. The start of the widebody.
Having a 25' unit I can wholeheartedly suggest the following:
Do not get the non CCD/Classic windows. If you are new to Airstreams, you can tell the HEHR windows (the junk ones) by the outside, they have black frames. They leak air everywhere. The good windows are the ones that the whole window opens and closes and do not have a black frame around the outside of the window. The good windows are found on SE, CCD and Classic trailers. I custom ordered my Safari and was told no way they would upgrade (for additional price) the windows at the time of build, but that was 2004.
Get the second fantastic vent installed in the back. If you get the LS package on the Safari, or now called the Flying Cloud line, it comes with a spare tire and carrier, upgraded faucets and the front fantastic vent among a few other odds and ends included in the LS pkg. Having two fantasic vents really helps when you are in places without electricity and need good airflow inside.
Back in October 2003 I had pondered about paying the at that time $250 upcharge for the 15k BTU A/C unit. I had a 19' Bambi with an 11k BTU unit and it worked hard to hold it's own. Many folks here on the forum said it would be a bad idea. But then I looked at Airstream's own specs on the 25' Classic and found the 15k unit was an option for that. Since the 25' units are the same size no matter what 25' model you get, I went ahead and upgraded to the 15k unit, when my Safari was being built. The electronic controls for both the furnace and this A/C unit are excellent. In full sun and over 90 degree temps I can hang meat in my trailer if I needed to.
The unit does not cycle more than normal as was said here that it would, nor is it overkill for a 25' unit. The 13.5k unit that comes standard is a good unit, but it is not anywhere near as good as the 15k unit. I would NEVER buy a 25' or larger without a 15k BTU sized A/C unit. It costs pennies IMHO to upgrade as it's being built, but costs a LOT more to swap it out later. Ironically, in the past few years, there have been a lot more 15k units installed in the non-Classic trailers. There were none that I found back in 2004 on dealer lots, and even some hesitation at the factory to put it into a 25' Safari back then, but they did it and now it is very common to see this sized unit installed....but, on the non Classic trailers, it's not on the menu, you have to ask for it special if you are ordering one.
I didn't go with the awnings all around and I think I should have. If I had to do it all over again, I might do all the awnings. Not because it is hard to cool the unit with the 15k BTU A/C unit, but it also shields the sun slightly making it less intrusive inside.
I would not suggest adding or buying any RV with a skylight. I have heard just too many issue with the domes, and since I think they still install vista view windows, there is plenty of light inside. If they don't come with vista views, I'd see about getting them. They are great. They were not available when I ordered mine, but I will say, if they were, I would have gladly paid an upcharge for vista views.