You can probably go pretty far on just the stock ballast. By the time you're really ready to step up, you'll probably have people in your crew that can bring their sacks and pumps and help you get it dialed in.
But yeah, many of us end up with sacs filled by portable pumps (couple for either side of the engine and one in the walkway). Once you get it really dialed in you can clean things up by increasing the size of your stock ballast or plumbing the new sacks into the original equipment system.
Mine came without factory ballast and I use a 750-pound Big Bump all the way aft, sideways in a locker (it actually rides aft of the transom because the hull has an overhang) and a second one forward in the walkway. Nice balanced 1500 is fun for me, but others like much more weight in my hull (especially SAN folks). Carry two pumps and often run both at once - 1500 in about five minutes :-)
Others augment the water ballast with steel, and if you're near SoCal, check out Pop Products bags - they're 40-pounds of rolled steel shot-like stuff, in a fabric pouch with nylon webbing handles. I think some guys will put like 800 pounds of them in their boat to help. I have four, and love having them under the bow cushions. Very compact.
My two cents is don't worry about it too much if you're choosing one of the 'common' brands discussed here. Most of the good boats have enough stock weight to get you running, and like I said, you can always find a third with some sacks to check it up.