You will be ok. Just try not to go toooo long before doing the UCA. I went the same route you did. Put my lcas and brackets on last month, and will be ordering the UCA and mount next month. I have about 6k miles on the car since lowering, and no problems.
I definitely agree with Primer though. Do the work yourself and save some money. The LCAs are a breeze, and the UCA isn't bad at all. Just a little tough to reach the bolt.
2014 Mustang GT Base MT82 -Stock 3.73s, Roush axleback, Steeda 93R tune, Steeda Hi-flow X-pipe, 19" Charcoal AMR's, smoked front and rear side markers, 20% tint, quarter window louvers, Steeda Ultralite springs, Koni Str.t shocks/struts, MM camber plates, J&M adjustable panhard bar, BMR LCAs and relo brackets, Barton shifter and 2-post bracket, Black Modern Billet Grilles