Seems to me you have a really good handle on the double and treble crochet! Good job...(I couldn't do a treble forever until a friend helped me, I had read poorly worded directions LOL).
As for the chains...usually in a pattern it will say, ch 3 (counts as first double) so I always count it unless they say not to and this is the way i understand (even though i have been crocheting since i was 9, I am still 95% self taught and if I am wrong we will both learn something
) for double you start on the fourth ch and for treble its the fifth. Sometimes in patterns it will give you different directions, and if its a book or a mag they generally have an over view of the basic stitches and you can see how they generally expect you to do it in their patterns. I had a baby cardi pattern a friend passed along to me in which the directions were different then the way i generally hooked, and my stitch pattern never worked out number wise until i checked this very exact issue...after that my texture came out perfect and made an adorable sweater that made a great gift. Hope this helps you out
Welcome to the gentle art of hooking