What do you mean by it would be more complex if they move at the same time? Is it related with power through the board capability?Or the programming part?
It is the programming part as all the stepping motor libraries assume just one motor and getting two to move at the same time has to be done by hand, in a coding sense.
I would say get a Uno and learn to use it. Look at the learning section on this site, and then on to the playground.
Do a few projects first, then start your project one thing at a time. For example get the humidity sensor just printing out values. Write something just to move your motor. The combine the two to control your motor. That is never go for the big bang solution always work incremental testing as you go.