#1 They give a little more support but it's not a game changer and using the narrow type is ok if you have them or can't fit the wide ones in. If no obsticles then I'd always use the wide if possible, the price difference is nothing.

#2 Depends what your doing but Don't waste your money on Aluminium bed if your mostly cutting woods because most of the time you'll have spoil board on top. For the main base a good grade ply wood sealed is fine. Then put spoil board on top of this and surface that.
If you need the flatness of Tooling plate or surfaced aluminium bed and plan on using coolant all the time then you'll need something that's stable so spend the money but IME most the time you'll have spoil board on top. And probably screwing into it.?
Most common question I'm asked is "What do I use for work holding" the answer is "Anything that Works".!! . . . I'll Clamp, screw, bolt , stick or suck and often some combination of few of them just to get a job done. Thou by far the most common is screwing down into spoil board.!