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Regarding time for casting to be complete. Usually, you’ll take the mould out of the machine when the spin cycle stops, put another mould in and pour the metal into it. Then, whilst the second mould is spinning, open the first one. And keep repeating the process.
Moulds are (relatively) expensive if you are not making your own. Metal is a biggish outlay initially but you price your figures accordingly. Is the machine expensive? Well, that does depend on how much you pay for it. Not being funny. A new machine is obviously a lot more expensive than a well-used secondhand one,
I am not familiar with the machine - is it a compressor or a bob weight machine? Compressors are much easier to operate without having to fiddle settings.
You say there are various moulds - is this a proper range of figures? Does the person selling them have the rights to do so? it is worth checking.