Hey there, you can definitely go and edit to add photos and other things, as long as it's within the 7 day timeframe.
One of my local steemit friends wrote this excellent post that explains in simple details how you can edit markdown on steemit.
I would also like to make a suggestion that you and @valblomqvist get yourself familiar with @minnowsupport and join @aggroed's Peace, Abundance, Love channel on discord chat here https://discord.gg/HYj4yvw
There is a whole community of us there who are helping one another on steemit and we would love to have you.
Thank you!!