Small warning about those models, they are optimized for mobiles, not necessary for huge open worlds. So you need to code and optimize level streaming.
I bought some packs from them and models were split into multpile objects (ie. more drawcalls), this is fine for small scene for mobiles (more drawcalls but simple shader). While in big openworld you have lots of drawcalls already, and on PC that difference in shader complexity is not noticable. So you probably need somebody who can do level design, and optimize all those meshes for big open world.
Anyway Synty Studios is most complete set of meshes for a game avaiable on unreal marketplace.