Lot of info on this scattered in past threads, but it depends on several factors. Any idea what the payload is on a typical Timberline?
You'll want to stay under 6,500 dry and will want to have a really dialed in weight dist hitch, shooting to keep the hitch weight at the spec of the trailer and not going over the payload and axle capacities if you can help it. Personally I would stay under 30' overall length.
With 2 of you and just 3 dogs you have lots of options out there. I tow a 30 foot (27ft model), 6400 dry capacity trailer with dual slides and a kitchen island. It's a great size for 2 of us and 2 large dogs. I'm at the absolute limit of my older 2010 Expy in my opinion, and that's after upgrading several things such as sway bars, spring spacers, and a very good understanding of using CAT scales to weak things. It took over a good year of trips to the CAT scale that I finally dialed in the weigh dist hitch and moved cargo around the trailer to be exactly perfect for my set up.
There is definitely a learning curve, but if you put in the effort upfront it'll make all the difference later and how you'll feel comfortable on trips.