To answer your question about accessories for the mount , saddle , hooves ect. On your first teir mount which is the initial purchased one,that will only allow the use of the green accessories. Once you collect 20 more mount shards , 30 green pills I think it was, along with the green accessories then you can Teir up. Its essentially an evo like a pet which turns your mount quality to blue. In turn,then you can collect and use the blue accessories. On a side note the accessory stats wont count into your mount until you teir up. Whether you plan on teiring up or not is entirely up to you but its always good to have the stuff done just in case. Blue teir is another 50 mount shards btw , so it's going to be a lengthy process either way
You can always collect the next color shards to get ahead of the game . Once you synthesize them they get sent to your mount inventory for later use.