I sense some confusion here on GVWR. There are two different GVWRs involved, the trailer and the tow vehicle. In each case the GVWR specifies the maximum safe weight of that vehicle. The trailer GVWR directly relates to towability, but the tow vehicle (the Edge) GVWR plays only indirectly.
The trailer tongue weight is the amount of weight the trailer places on the tow vehicle's suspension. That tongue weight becomes cargo as far as your Edge is concerned. For estimating purposes, assume the tongue weight will be
10% of the trailer GVWR. In actual use the tongue weight will be 10-12% of the actual trailer weight, but that can only be determined later on a scale. Use the 10% of GVWR estimate for now.
The tow vehicle GVWR doesn't play directly in a towing estimate, but it is the governing factor in determining how much cargo the vehicle can handle. You already know what that cargo capacity is - the 950 lbs shown on the Edge door placard. That 950 lbs represents the upper limit for everything carried in or on the Edge - passengers, gear, the trailer hitch itself plus the trailer tongue weight.
There are two weight factors that affect any type of towing: (1) The total trailer weight that must be pulled down the road and braked to a stop, and (2) the portion of the trailer weight that rests on the tow vehicle hitch (the "tongue weight"). For recreational trailers, there is a third factor, the wind resistance of the huge frontal area of most RVs. At 30-60 mph, that frontal area wind resistance acts like additional trailer weight. When Ford (or GM or Ram) gives a tow rating, it is a general one for all trailer types and not specific to RV trailers. Therefore, for an RV it is wise to keep the actual trailer weight below the tow vehicles max limit.
I want to make sure that I fully understand that it will be able to COMFORTABLY tow the travel trailer. I would actually like a bigger trailer (GVWR of 4745), so am looking at something with a V-6 that is rated to tow at least 6,200lbs. Is that reasonable?
Yes. If you shop for a trailer that has a GVWR that is no more than 80%-90% of the tow vehicles max tow rating it will probably be OK. However, you will want to do more exact arithmetic once you have narrowed your choices down. Use the "rule of thumb" estimates to sift through what is available on the market but don't commit to a purchase without doing a more careful analysis. The reason for that is there is a mixture of fixed and variable weights involved, so that the rule of thumb percentages get less & less accurate as trailer weight increases. Further, the wind resistance factor doesn't change much with trailer weight.