I like to give a new horse a few days with a fence between the new horse and the heard, just so they can settle in and get to know each other without the risk of the new horse having the cr*p beaten out of him :/ He can retreat and have his own space while he is feeling unsettled. Its also useful if the barn you are going to wants to quarintine the new horse for a week or so- some do.
As far as riding, give it 3 or for 4 days probably. See how he seems to be settling in. Its also important that in the first month or so you are extra vigialent about behaivoir, as this is when the horse will test you most to see if you are up to being his momma!
Congrats on the new horse- he's a real nice looking horse, and welcome to horsey ownership!
We lose ourselves in the things we love, we find ourselves there too ~Kristen Martz