Started off with a soundcard scope in 2007, then a £25 USB one in 2010, then a £50 USB one last year and today i'm getting a Rigol DSO1054Z 50MHz, can't wait
i'm predicting few months or just weeks from now, you will get the real real scope, something like 5-6GHz 20GSps scope
the "Moving Forward to the Future, Breaking GHz limit" slogan for hobbiests
i've read that each probe should be calibrated with each BNC input, is that right, 16 calibrations for a 4-channel?
yes and no. yes if you keep swapping probes between channels, in this case not 16 actually, it depends on how much you swap them, it can be 100... with 100 times of changing probes. and no, if you stick one probe to one channel, so 4X compensation only once in a lifetime.
i think you are referring to higher end scope, like the GHz scope, because it can recognize different probe's ID. and each probe has memory to store calibration for each channel it connected to. for Rigol probe nada, its just a passive probe.