It's not uncomen for me to have 3-4 builds going at one time. What helps me keep track of things is to check off on the instructions what has been done. The other is that I keep parts and assemblies in a box top or bottom untill they are ready to be glued, painted or workind in some way and then they go back in the box. Once ready for attaching to the main model body they come out of the box for the last time.