I should preface that this is not supposed to be a full flight simulator. That means, the simulation is not made for larger heights and velocities. There is no supersonic regime. The air drag just gets lower and lower the higher you fly (using the barometric formula). The focus is on the ground operations: stacking, launching and catching. You can fly above 10 km and more than 300 m/s, but it's not accurate. That's also why you can just skip boost back and initiate landing directly*. It allows to rapidly retry the catching, because it's not easy and it might take a bit to get a hang of it.
With the current setup the main challenge, besides catching, is to find the exact time to start the raptors. Also, with the booster you have to switch off some engines during the process if you land with too much. I am not sure, if I keep it like this or make it automatic as well. It was more challenging before I implemented time scale adjustment. I guess, it's up to you, if you want to go hardcore realism mode and always use real time :D
When you change the starting location, the booster will be orientated towards the landing target automatically. But you have to set the horizontally velocity accordingly yourself so that it actually arrives there. This is a bit trial and error.
If it's too difficult you can reduce the downrange distance and set the target position to 0,0.
Also, you can move the catcher arms with the keyboard. The keys are written on the control panel buttons (English/German keyboard layouts). This helps a lot.
In the future I might add a timer from initiation of landing, to full stack, to reaching 10 km or so. So you can try to get the quickest turnaround time using the smallest amount of residual propellant.
*with the current manual control it's almost impossible to do a proper boost back anyway