Your choice of equipment sounds like a really good plan to me. I think that in the end you would be much happier with the system if you made 2 adjustments to your plan, and I'll lay out a couple of ways that I see to do it.
You could use the M700/5 to run everything, as you planned. That would give you 100 watts x 2 on the cabin speakers (50 watts per speaker), 75 watts x 2 on the tower speakers, and 180 watts on the subwoofer. In my opinion this is a little light on power, but it will work.
The 2 adjustments that I would suggest are:
1) Plan for an amplifier dedicated to the tower speakers. Even if you don't do it now you can design the system with that upgrade in mind by fabricating an amp panel large enough to mount an additional amplifier and 2 distribution blocks (if needed).
Also, if the power/ground cable run is a long one go ahead and run 2AWG cables now instead of 4AWG cables so that if/when you decide to add the tower amplifier you already have the correct gauge power/ground cables to support 2 amplifiers. If the power/ground cable run is a short run you could skip that step and just run an additional 4AWG cable run when you added the second amp.
For the second amp I would suggest the JL Audio M400/4 bridged into 2 channels, giving you 200 watts x 2 on the tower. This would also mean the M700/5 would be putting out the full 75 watts x 4 to the cabin speakers, which is 50% more power to the cabin speakers than if you were to run the 4 cabin speakers off of 2 channels of the M700/5.
2) Upgrade those tower speakers from the cheaper MX Series to the slightly more expensive but much better suited for the tower M Series. The additional up-front investment in the M Series will really make a difference. The M Series has a 1" dome tweeter versus the 3/4" dome tweeter of the MX Series, and while the MX Series speakers are great for in the cabin, the smaller tweeter just doesn't project as well in a tower application.
That gives you a 2-stage plan where you can try it with just the M700/5 and if you decide that you want more performance you are already set up to add the second amp. But definitely consider the M Series for the tower, you will be glad you did.