Yes, 3 monitors in Linux can be done, and it is fun! (I have 4 monitors in front of me right now), but there are limitations forced on you by the hardware you are suggesting. It may not work the way you want.
Let me explain:
In Xwindows, all the monitors that are hooked to 1 video card can be combined into a big, single Xscreen. So you can move a window from 1 monitor to another on the same Xscreen, or expand a window to span the whole Xscreen. You can have a second video card and have more monitors hooked to it, but they are seen by Xwindows as a second Xscreen. On that Xscreen, you can move windows around across mujltiple monitors, but the windows cannot leave that Xscreen.
Most software works fine with 2 or 3 Xscreens, but a few programs will not let you have an instance of their program on each of 2 Xscreens at once, you have to close one to open it again on another Xscreen. Not many, but there are a few.
While your cursor can move across all monitors (on all Xscreens),dragging windows across Xscreens will not work.
To get 3 monitors working as one big Xscreen, you have to have a video card that has 3 video outputs on the card.
Be aware that there are some video cards that have 3 ports but only let you use 2 of them simultaneously. Read the fine print carefully.
Currently there are several ATI cards that do up to 6 monitors on one card, which allows you to have up to 6 monitors as a single big Xscreen. I prefer nvidia cards, but alas, there are currently no nvidia cards that support more than 2 monitors.
Also, the three monitors in Linux will only help you if you are running in Xwindows. Even if you have 3 monitors hooked up, when you working in a console, you really only get to use one monitor. It is possible to have the FB console show up on two monitors, but only as clones, so you are looking at the same thing on two monitors, and the extra monitors sit there, black.
Since you are going to be spending significant money on hardware to accomplish your goal of making your computer into a workstation,you might consider getting a 30" monitor instead of going with two or three smaller monitors and two video cards; it gives you a big screen at the console, a big screen in Xwindows, and no worries about configuring and setup, just plug it in.
I am not sure what you are wanting to do, and what exact hardware you are trying to work with, so I tried to mention some issues to think about before spending big money.
Good luck, and lots of fun to you!