To hold the fabrics together, you can try safety pins. They sell really tiny safety pins as well as the large, so you can gauge which would be most helpful. An assortment pack might be good. You can use straight pins but you might get poked a lot.
The other thing you can use to hold fabric together is double sided adhesive tape, like the kind you wrap presents with. You can get that at an office supply store. Craft stores sell some double sided tape that you can leave in the seam and wash out later, but that's not necessary here. It's easy enough to remove the tape once you sew the seams. Another thing you can try (but last choice on the list) is water soluble glue stick. Always test the tape and glue on scrap fabric first. The glue stick (and maybe tape) might be a hassle to remove, so test first and consider carefully. Also, if there's any stickiness on the fabric, it might gunk up the iron. If you use that iron for other clothes, that might be something to consider.
If you're going to iron the seam to one side, iron it open first. It sets the stitches and is easier to get an even seam than if you iron it to one side from the start. If you iron the seam to one side, the fabric might bunch on one side so you'll have to gauge which seams will go which way and test it out.
Edit: I'm going to take back that last part about ironing the seams open. When I looked it up, there's controversy about it, so I guess it can go either way. Controversy about sewing. The internet truly is an amazing place. Here's someone who irons the seams to one side and gives reasons for it.