I am doing 4 tiers (14, 12, 10, 8 ) of 4" high each and they will be lined up on the back side of each tier. If I use SPS will this hold up okay, or is it going to fall backwards? I'm very uncertain about this and would appreciate any helpful comments!

I just did a three tier like this. Yes it does hold fine but you have to make sure everything is super level and you need a small or flat border so it doesn't extend over the edge of the cakes where they're all lined up. I don't use SPS but double center-doweled my cake to make sure that there was no shifting in transport. I used the hollow plastic Wilton dowels in my cake.

And, yes as Anna mentioned, make sure that your supports don't get too close to the edge of the cake - I think SPS is ok in this regard. Also I used ganache and fondant which helps keep everything firm.

If those cantilevered cakes can make it than this can...I had no troubles with it. Good luck.

Thanks for the tips!

I would be tempted to put every other support plate as far to the front as possible to help balance the weight.