oakman

Vertical rebar in the middle looks like a bad idea. It will get in the way of shovels when you will be spreading the concrete. Less of an issue with a pump, but you will still hate it when you'll be making it level after you pour. I made marks on sides of trenches as a rough indicator, then used laser and a ruler. Got level it all level to 1,5 cm. BTW, pumps are generally expensive and for trenches often unnecessary.