You can’t span 19 feet between supports like that most likely, espescially outside. Most glue lams aren’t even made for outdoor usage. According to my stepdad, a carpenter by trade. Maybe your lumberyard will tell you otherwise.
We’ve run glue-lam headers of over 16 feet, but there aren’t people standing on them all day long either. 2x8 joists will only give you a ten foot span, but if you put your beam 9 feet out you can hang them two feet off of the end of it. 2x6 decking is unnecessary, you can use 5/4 x 6 decking on 16 inch centers. its rated to 24 inch centers, but i’ve heard tell that that gets spongy. 2x6 I THINK is rated to 32 inch centers. Some guys do like to use 2x6 for their decking, it makes it infinetly stiffer, but 5/4 is stiff enough for the money if you want my two cents. (my 2 years experience two cents, i’ll add)
as to your beam, a doubled up 2x12 is what we usually use, you have 8 feet between posts there. i THINK you can do the same with a doubled up 2x10 beam. Is there an issue where you can’t or don’t want posts at your beam line? you could run your joists parallel to the house, between two freestanding beams, with 2 x 12 joists you have 14 feet, and two feet cantilevered on the other end brings you to 18 feet, you could cheat 6 inches on your span and 6 on your cantilever for your 19 feet, or you could put them on 12 inch centers for a longer span (though i don’t know what that length is). Something like that might be a great time for 2 x 6 decking. How high off the ground is this?