TS,
both are excellent cameras. mp is not necessarily better built than the m7.
The main differences and plus and cons from my experience:
M7 has aperture-piority. very useful feature if you are those auto-universe shooter. But take note metering is still robotic, it cannot tell if it is the darker face you wish to expose for or the back ground light just like any system. So dont depend on it under tricky light condition unless you know super well how the AE of this camera expose. This comes with time spent with it. Of course you can shoot manual with it. But I always feel weird to have something on my camera I dont use.
MP has the classic rewind knob. Its awfully slow compared to the newer designs. But it wouldnt break like the newer design due to tension or film jam, just slower pace and tired fingers. Also it is not like the old M3 style where it will auto rewind back due to tension. MP's design has grip. You can pay $179usd and change to another rewind crank but its a silly design and will likely scratch your top plate. I find it ugly and silly, dont bother.
MP viewfinder is brighter and less prone to flare than M7.
MP has no ugly red dot. But to each his own, some actually like the red-dot.. you know.. those leica snobs.. hehehe
MP typically spots the new sharkskin covering versus the M7/M6 leather covering. It provides more grip and wouldn't peel as application is a pain-staking melt and apply and harden. cons is that it will be difficult to remove if you wanna change skin next time.
M7 has electronic boards in it, so any part down isnt as simple as mechanical $_$
MP has a all metal film level like M3, M7's is half plastic like M6 to save cost.
My take - if you like to like modern way of shooting fast or lazy to meter. M7 is for you. It can be counted on mechanically. MP is not a camera that tells you what to do. You decide for yourself how much you wish to expose a scene, you are the master decision maker. MP is not technological sophisticated but it is more an emotional side of things. I for 1 like more emotional attachment in my daily object.

I have seen people frustrated with MP and sold it for M7 instead and some find M7 too "robotic" and wanted something they can pass down to their sons, and got the MP instead.
either camera, you cant go wrong. good luck and welcome to the club :thumbsup: