A great big welcome to the Forums, Johnny Miller. You'll find all the info you need here. Use the search function to locate many past posts on the issues that you are asking about.
Here's my read on what you are asking.
For 2 1/2 people, the 19' foot is probably better, especially since you want to work out of it. The 16' does not have separate black and grey water tanks.
Winter camping is possible. Airstreams are really quite cozy if you are set up properly.
If you don't feel that your van is reliable, you definitely need to upgrade. The trailer brake controllers can be moved from one vehicle to another. Make sure that you get plenty of truck for the job. If you don't, you will not like towing. A full size Toyota can probably handle a 19' Bambi, but not much more. Keep in mind that Toyotas come only in a half ton version. Three quarter ton is definitely better for any heavy towing job. All components are beefier on a 3/4 ton truck. Remember that when pulling a heavy tyrailer, towing capability trumps fuel efficiency.
SuEllyn & Brian McCabe
WBCCI #3628 -- AIR #14872 -- TAC #FL-7
2015 FC 25' FB (Lucy) with HAHA
2005 Suburban 2500 Quadrasteer (Olivia) & 2011 Silverado 3500 (Fred) with Outfitter Truck Camper (Ethel)