In embedded applications, there are two typical approaches to starting your processes at boot time.
One approach is to run a shell script that contains the command lines for running the processes. There are some useful utilities such as on and nice for controlling how those processes are started.
The other approach is to have a starter process run at boot time. This starter process then starts up all your other processes. This approach has the advantage of giving you more control over how processes are started, whereas the script approach is easier for you (or anyone) to modify quickly.