I didn't stack the CM 4228, only used one. It's hard to stack because of it's weight. In fact, one 4228 was more stress on my rotor than my current Yagi stack. If you're interested in stacking, I'd go with a Yagi of some type.
Candidates include Televes DAT 75, Triax Unix 100, Antennasdirect XG91 as well as Winegard PR9032, CM 4248.
Horizontal is the way to go if you want to narrow the horizontal beamwidth . Vertical stacking narrows it vertically. The problem with vertical for me was the long lever arm required above the rotor. It just won't hold up over time unless you have a heavy ham rotor or a thrust bearing.
Combining the antennas is easy. You need exactly the same length coax into a wideband combiner(splitter). Zenith actually makes a pretty good one that is sold at Lowe's. I use a stripline combiner from Lindsay Electronics but honestly the performance is only a little better than with the Zenith (about 7 bucks if I remember). Your spacing (horizontally) with Yagis should be b/w 46-58 in. or so. Spacing with vertical stacking is around 40 inches. You play around with the spacing some to see what works best for you. The antennas need to be aimed in exactly the same direction in both horizontal and vertical planes.
What takes some creativity is making the mount. Vertical stacking is easier because you simply mount to a mast. Horizontal involves figuring out a mount that is sturdy and any supports perpendicular to the signal in the horizontal plane need to be non-conductive (i.e. wood or fiberglass). Fiberglass tubing/rods are available from Max Gain Systems in various sizes/lengths.
You probably don't want to hear this, but the first thing I'd do if I were you is go back outside. I'd recc. try a single high gain Yagi first then you can upgrade gradually if you get the itch. If you really want to go with an 8-bay, the CM4228 has better gain across the uhf band than the Winegard 8bay. The Antennasdirect DB8 is supposed to be the best 8 bay out there, but it is at least twice as expensive as the 4228.
Some comparison gain charts on various antennas you might be interested in can be found athttp://www.hdtvprimer.com/ANTENNAS/comparing.html
P.S. Commercially made mounts for horizontal stacking are available if you don't want to DIY. One source is http://www.atechfabrication.com/reception_solutions.htm