Engineering Project

I am part of a team of engineering students who are new to drones. We have been tasked with building a hexacopter survey drone and are going to be using the Pixhawk 4 with obstacle avoidance using MB1242 I2CXL-MaxSonar-EZ4. We want to use mission planner so that we can tell the drone to take photos to use in photogrammetry and also geotag the photos. Since we are inexperienced, we have a few questions.
We understand that we can set up basic flight functions with the PX4 software that would be installed on the Pixhawk 4. In order to use mission planner, do we have to upload it to the Pixhawk 4, or do we need to only have it installed on a computer?
Is it required to use a companion computer to have simple collision prevention when using the MB1242 plugged directly into the Pixhawk 4?
If there is a planned mission and an obstacle is detected, will the drone know to go around the obstacle?

Thank you,
Alex Segal

PX4 is a firmware loaded on the flight controller, as is Ardupilot.
The ground station software you use for config may depend on the firmware in use on the FC.
For example, MissionPlanner only works with Ardupilot, but QGroundControl will work with both PX4 and Ardupilot. The ground station software is typically installed on a laptop for portability, and there’s ways to use either Windows10 or Linux (mostly Ubuntu).

You need to look at the firmware features and make that choice first.

My personal view is that PX4 and QGC are a bit quicker and easier to set up. MissionPlanner and Ardupilot have many more features, options and intricacies and they will take you longer to learn and get things working - but that journey could be worth it for you.