If I could rewind time, I'd buy lightly used for my first TT. After your first few trips, you will quickly find things about the floor plan and features you like or don't like, and will probably want to upsize/downsize, or will want a different floor plan after your first year. You'll be wise to keep the dry weight under 7000lbs, anything over will be scary and a burden to pull with the Tundra (I have one too). I strongly suggest upgrading your tank to the 46 gallon transfer flow tank, otherwise you'll be stopping at gas stations every 150 miles or less depending on the grade you're driving on (not kidding).
Grand Design is nice but you'll need to stick with their Imagine series, as the Reflections will be too heavy for the Tundra. Check out Jayco, Starcraft, Forest River, Outdoors RV, Northwoods, and Heartland. I always hear bad things about Keystone quality so steer clear; you've got plenty other choices.
Premium features that aren't standard on all trailers that I like are: solid fiberglass side (not the siding shingle type), slam latch cargo doors, dual pane frameless windows, solid surface counter tops with undermount sinks, 8cu.ft. fridge, convection microwave, thermostats that automatically control furnace and AC, quick disconnect LP lines for bumper mounted Aussie Grill, pre-wired for generator, solar , and backup camera. Last but not least, rack-and-pinon slides, stay away from Schwintek, they're notorious for leaking and aren't as heavy duty as rack and pinion type.