I found a flight on Continental's website from Houston to Edinburgh with a layover at Newark. The connection time is 2 hours.
First, is this sufficient to stretch our legs, grab a snack, and switch planes?
Second, The arrival time is 7:40 AM. Is this the time in Edinburgh? Or do I need to add the time difference?
Third, the two planes are a Boeing 757 and 777. I've seen some users compare the different airlines and plane types. What should I expect? Are there certain things to look for?
Please pardon my ignorance...neither I or my sister (my travel partner) have attempted any of this before.
Thanks in advance!

1. Yes, that's more than enough time. All CO flights from Houston to Newark arrive in Terminal C, which is also where you flight to Edinburgh departs. Even an hour is enough.

2. Yes, 7:40am is the local time for Edinburgh. Airlines always give you local times.

3. Huge difference. The 757 across the Atlantic is terrible in coach. 3-3 seating, with only one aisle and lavatories for coach passengers are only in the back. Plus, no personal video screens for coach. It's a huge step down in terms of experience compared to CO's 767 and 777 to Europe. However, EWR-EDI is also a relatively short flight (at least for the outbound).

So, do I take it the higher the model number the newer the model?

Kind of.... Really, the model number here matters as far as cabin layout. The 757 is a single-aisle plane-- one aisle, three seats on each side in coach (cramped!). The 767 was certified practically simultaneously to the 757, but is a larger, two-aisle plane. The 777 is quite recent and even larger, and two-aisle as well.

[The number system breaks down a bit with Boeing's 717, which is "new" to Boeing but really a brand-new McDonnell Douglas DC-9-30 (closest size variant). The soon-to-be-released 787 sets the numeration world right, thankfully.]

CO flies 4 models of planes across the Atlantic.

The 757-200 is a single-aisle plane, with 3-3 seating in coach, and no personal video monitor. CO only recently starts flying this plane across the pond, but are using it more and more often to secondary European destinations.

767-200 is an older 2-aisle "widebody", with 2-3-2 seating. All seats have personal video monitors. Some think the 2-3-2 seating is the best, as only 1 in 7 person has a middle seat.

767-400 is the newest model in CO's fleet. Longer than 767-200 with higher seating capacity. Comfort/amenities is similar.

777-200 is the "flagship" of CO's fleet, the largest of them all. The planes are relatively new, with a 3-3-3 seating and personal video screens on every seat.

Thanks everyone.
I will keep this in mind. I'd like our first trip across to be as comfortable as possible.

It will be a tradeoff - less comfortable in coach on a 757, but if your destination is Edinburgh, you won't have to go through plane changes, buses to trains to trains to taxis, etc. in London or elsewhere. The direct flight will shave hours and hours off your itinerary, time that you can use walking up Arthur's Seat to get the kinks out of your legs.

CO also flies to GLA, with a 767-200.