That's your first go!
Is there anything you can't do?
I think it looks lovely, it doesn't matter about using thicker or thinner thread, if the piece comes out a little bigger it's fine. I think the the picots are dine, I'm impressed by joins to. Picots are a matter of preference, and I like yours, you've got them coming out the same size, which still
find hard to do.
You work your ends in just like knitting, although for that your going to need either a very fine crochet hook, or a sewing needle with an eye large enough for your thread.
You've done a lovely job, well done.