My 1989-vintage Ron Charles Vacuum Forming machine has a 9x12 inch platen that is simply perforated steel plate, there must be well over a thousand holes in it. For suction, it uses, believe it or not, the motor, impeller and volute unit from a Kirby Vacuum Cleaner, which moves a helluva lot of air, very quickly.
For successful vac-forming, it's necessary to remove the air between the hot plastic and the platen & master fast, fast enough so that it sucks down the hot plastic almost instantly, before it has a chance to cool. You mention .75mm styrene, that is the same (for all intents and purposes) as .030" thick, and that thickness of styrene is eminently formable by vacuum, provided it is hot enough (it should be as soft as a sheet of soft rubber!).
Laboratory vacuum pumps are fine for many things, but vac-forming really isn't one of them, as lab pumps are just too slow. They get their advantage by removing air slowly, but completely, to at least 29" of mercury, which I understand to be a mechanically perfect vacuum for most applications.
Take the advice you have already gotten, use a shop-vacuum to extract the air, those are more than powerful enough for vacuum forming, and certainly quick enough, due to the volume of air they are capable of moving per minute--lab pumps are not, from all the lab pumps I've seen.