Hi!
I'm a fairly new user of gmail too, and I just looked at their 'help ' section and found the following:
"Adding or sending attachments
It's not possible to add or remove attachments when composing a message in the Gmail mobile app. However, if you forward a message, the Gmail app will keep and forward any attachments from the original message. The attachment will not be included when replying, only when forwarding."
Perhaps gmail's not your best bet if you want to send lots of attachments.
If you want to send photos, you need to start from within the photos app. Open the album containing the photos you want to send, tap the arrow button ( top right), tap the photos you want to send (up to 5 at a time I think), then tap the 'share' button top left. Choose 'email', then you can send your email as normal- your photos are already in the email before you start typing.
Hope this helps!