The flyer seems to be a little larger than a runabout - she is roomy and fast enough to do short interstellar trips, but seems to lack the largish rear compartment of a Runabout. Instead the extra volume appears to have been given over to bigger and better shields and weapons. All of the canon (yellow text) details on the specs page come direct from "Extreme Risk", although I'm not 100% sure whether the parametallic hull plates were used as well as or instead of the tetraburnium alloys. The flyer was stated to have a "Borg-inspired" weapon system, and Tuvoks unimatrix shielding - the latter is presumably also based on Borg tech, although it's hard to say.

In part the Flyer seems to me to be an acknowledgement on the part of the creators of just how many shuttles Voyager has lost over the years - not only do the crew admit on screen that their shuttles have not been up to the job, but by making such a big deal of the flyer we can be fairly sure that the writers are not going to be blowing it up any time soon!

The timeline for the building of the Delta Flyer is not completely certain - Paris said he could have the ship done in a week, given that he had already done considerable work on the design. How much initial work he did is open to question - I can easily imagine him fiddling around on something like this in his spare time over the course of years. On the other hand, the design was sufficiently incomplete that several fundamental design factors were suggested in the initial meeting on the flyer and as of the first design meeting on the ship they hadn't yet done the thruster specs and hadn't decided on the basic hull materials or shape. In addition, the episode indicates that they were able to finish the flyer about 36 hours ahead of schedule. Given all this, I don't think it's unreasonable to suggest that a typical starship could complete a project like this from scratch in around two or three weeks - call it a month at the outside. This is a shot in the arm to the extensive speculations I have made in the write ups for the Type 9, 10 and 11 shuttles regarding Starfleets gradual move toward allowing ships to work on just this kind of thing as a matter of normal routine.