Start HERE for catalogs of just about every year of post-war Chicago Schwinn:
http://www.trfindley.com/pg_schwinn_cats.htm
Those catalog links will cover most everything, but a couple of them are early or late year catalogs and a few models are left out. Notably in '77 some colors were produced, but dropped mid year. Like Canary Yellow (pale yellow) and Flamingo (bright pink). Not all colors were made for all models, and once in a while you will find that a bike might have been made in an alternate color to what's in the book. There are also custom jobs, promo's, dealer-built bikes, and pretty darn good fakes out there.
For you, finding a nice '78 should not be too much of a challenge. They're out there, and not seen as being extremely collectible... not any more than any other base model Stingray. The color selections might not be people's favorites either.
I think in '78 you can get a regular or 5-speed Stingray, or a Hurricane 5, or a Scrambler/BMX based on the Stingrays' cantilever frame. (That's what the frame design with 2 curved tubes running from seat-stays to just below the head tube is called.)
There is a significant difference you'll have to take note of: Single-speed and coaster-3 hub equipped bikes use the "standard" frame, and the rear arch is not made to mount caliper brakes. Regular 3-spd, 5-speed, and Krate models do use caliper brakes and therefore have a plate welded into the upper rear frame that's much bigger than the little arch for mounting just a fender. Note that "Deluxe" models were made both ways, so there are models with fenders that do not take caliper brakes, and others that do. I would guess that 3 out of 4 Stingrays were standard coaster models.
The 5-speed Krate models were built on the same frame as 5-speed models of the day, and for years when coaster Krates were made, the frames are likewise the same as the standard Stingrays offered that year.
Krates are equipped with a springer front fork, fitted with a 16" front wheel on a 24" fork, and a 20" S-2 rear wheel. Coaster models used a Bendix coaster hub, either a RB2 red-band, or from 1971 on, a Bendix 70. 5-speed Krates feature Weinmann hand brakes and frame mounted shifters. Coaster Krates use many of the same parts but come with no hand brakes and no shifters.
The production of Krates starts in 1968, offering Red, Orange, and Yellow bikes: Apple Krate, Orange Krate, and Lemon Peeler. In 1969 the campus green Pea Picker appears. In 1970, the white Cotton Picker joins the lineup. In 1971, the Grey Ghost is offered, which is painted with the same silver that is the base coat for the red or green bikes, just clear coated. In 1972 the Ghost and Cotton Picker are dropped from the offerings, and the remaining bikes gain a rear disk brake. The Orange Krate's color also changes from the bright "Kool Orange" to the darker Sunset Orange. Other Schwinns using orange likewise change their color that year. After 1973 the Krate line is dropped entirely, though Stingrays continue until 1981, and Fastback models continue until 1976. All of the multi-speed bikes from 1974-on use a thumb-shifter mounted on the handlebars instead of the top tube mounted big Stik-shift.
There's a partial summary... any more questions feel free to ask.
--Rob