) I was wandering if there is a possibility to activate the sonar on it for testing purposes only?
For work in the city I will surely get a lidar.
2.) can the PX4flow sensor be used for precision landing? It can see IR light source accurately so theoretically it should work. If yes, what do I need to do?
Please note, that MT9V034 image sensor used in PX4Flow is not a best choice for precision landing task due to resolution, which is 752×480. Also you will need IR pass optical filter.