Arduino coding, programming

I have the robot consisted of 4 stepper motors, few sensors and controled by arduino mega.I need 5 different sketches to be combined in one sketch and here different sketch or group of sketches to be executed, when particular button on remote control is pressed. For your job cost evaluation below are the sizes and short description about these codes: Motor (stepper motors move to home position checking home position sensors)- 8 kb. Will be used when code is interrupted by electricity interruption or from start. I will give detail info about that. Finish (stepper motors move to home position without checking home position sensors – it just runs to primarily defined position) – 9 kb Scanning (robot moves to primarily defined xy points and at each point ultrasonic distance sensor scans z values and fills z array.)15kb. Random movement pattern by some direction. Robot moves by random movement pattern filtering out some z values- 15 kb Snake movement pattern. Robot moves by snake movement pattern filtering out some z values - 19kb Almost every sketch has the same void setup variables and functions, so when you connect everything in one sketch the overall size will be much smaller. I want implement commands for 8 buttons. these task include setting different speed, play/pause, execute command after 10 minutes, etc. I will give detail information regarding every task for each of 8 buttons. You need to have arduino mega board for testing due to size of sketches. I attached circuit diagram.