The amount of pressure is adjusted by how much increase from the previous shim behind the broach is. If you are taking a thicker cut, then more pressure is required. If the shim is is a very small increase from the previous shim, then the pressure is less. As long as you don't get greedy with your cuts, the pressure will be low. This is true whether you are using a hydraulic or not. Alignment is important, if the broach is "cocked", then pressure will be sky-high, even with a small cut.
If you have a lathe, you can always use it to do a one-tooth shaper action, and avoid expensive broach sets and arbor press. This is really only reasonable if you are making one-off parts, or VERY small batches. If you are doing production, then a broach, or a REAL shaper is the way to go.