Before you spend any big bucks on vacuum systems, learn a lot about them. There are many ways to go at it, some very inexpensive and well documented on here.
It depends somewhat on what you want out of a vacuum system, if you are holding large sheets that you will never cut through, you dont need much. However if you cut through the material it doesn't take a very big hole to let 20 or 30 cfm of air leak through. The vacuum level drops then also, and may drop quickly.
Dedicated fixtures with gasketing may be able to hold high vacuums with almost no leakage at all. For my first several years that was my preferred method, I used air-conditioner vacuum pumps and got remarkable hold-down for reasonable prices.
Later I wanted more tolerance for leaks, so I went to an industrial pump so I get the best of the high flow and high vacuum worlds. Most of the time the system operates above 20"Hg. Much as it was with the cheaper a/c pumps.
I have not used a blower, they are good when you are going to be cutting through a fair amount. You can look up on the forum where there are several designs using vacuum cleaner blowers, which by switching between series and parallel operation allow you to switch between high CFM and "better" suction.
Blowers usually peak out at about 15"Hg while offering 150+CFM open flow. This costs 15hp of electricity and noise in your shop. The pump I use is a 5hp Becker which offers 28"Hg and 75CFM open. Two of these combined would give 28"Hg and 150CFM open, better performance than the blowers for only 10hp of electricity.
No matter what you go with there are advantages and disadvantages.
If you are new to botting, consider just using mechanical hold-down until you have visited a few shops and seen what other folks are using and the results they get. Nothing beats mechanical hold down for the price, its cheap and very reliable compared to vacuum. I still use mechanical hold for many parts.
Hope that helps-
D
"The best thing about building something new is either you succeed or learn something. Its a win-win situation."
--Greg Westbrook