While martial arts can be terrific -- I've seen it build character and confidence in kids -- it may not be right for your son. Many posters are recommending it but from what you describe it might take him so long to warm up to it that he may end up feeling it's something he's being pushed to take.
Play to the strengths he already shows. You mention that he loves Legos and loves to build. I'd seek out a kids' Lego League in your area -- sometimes schools sponsor a Lego club; older elementary has something called First Lego League; or local libraries sometimes have building clubs or specific days when kids can come build; if there is a Lego store in your area (and I'm betting that in the Las Vegas area there is one!), call them and ask if they keep a list of local building activities, building "days" at the store and at malls and other places, etc. You might even find that you end up establishing your school's Lego club next school year....Let him do what he already likes and is good at so he builds up confidence in that, rather than putting him into another activity that's totally new to him.
Then, yes, introduce the idea of new activities later. I would look into whatever level of Boy Scouting is appropriate (or any other similar group). Seek out a small troop or group, and talk extensively to the leader about your son's tics and the importance of this troop or group being a place where he explains those things ONCE and it's done -- any good leader should be ready and able to handle the tics and shut down any teasing immediately. I recommend scouting or similar groups because they have varied activities that let your son try different things through the year -- but do check first; sometimes a troop will focus heavily on one area (for example, I know of Girl Scout troops that mostly camp and never do anything artistic, while other troops are all arts and crafts and never do anything outside--you want your son to get a balance). If a troop is very demanding, like a neighbor's son's Cub troop that camped every single month all year long, it might not be right for him. I might also seek out a small troop that already has a friend of his in it.
Be sure he has responsibilities. He sounds as if he might be the kind of kid who would do well being given tasks to do. If he already has regular chores, and does them OK, praise him and tell him you think he's a big kid and ready to do more; give him something responsible but also kind of fun and a one-time thing -- helping an adult clean out the garage; picking up every stick in the yard; going around the neighborhood or to a park with you, some gloves and a bag to pick up trash. Praise him. When school starts again: Ask the teacher at the very start to give him responsibilities in class and explain why he needs them.
What are your plans for him over the summer? Is he hanging out at home or doing camps--? I might ensure he gets enough down time and isn't overscheduled BUT I would be sure to schedule a lot of one on one play dates with other kids and have plenty of ideas in your mind to suggest to them -- at this age, play ideas can flag a bit and they might come to you saying "we're bored" but always have a suggestion. It's OK and it's not helicoptering to say, "Hey, there are about a million Legos in the living room -- why don't you see if you can build a bridge from the coffee table to the couch" or whatever! One on one playdates also will help him feel more confident around other kids.
I would be sure that he does get some kind of group activities over summer -- a one-week, half-day camp, for instance, or Vacation Bible School if that's your family's thing, or a weekly class (county and city recreation centers have lots of art classes, etc.). Be sure he does have some times with groups of kids so that he doesn't get so mellowed out by hanging at home he is in shock again when school starts.
Be sure to get on the radar of the school counselor! Do it now, even though school's nearly over. Meet with him or her yourself, with your husband or significant other present, but not your son; explain his tics, and how this year has gone, and get ideas from the counselor for summer too. Have your son see the counselor--many of them do a simple "lunch with the counselor" thing with small groups of kids each week, so kids are not intimidated by the counselor or think that seeing her always means something's wrong.
Then be sure to see the counselor again first thing in the fall and maybe set up a monthly (weekly, if things get tough) meeting for him alone with the counselor. An ongoing relationship with a good school counselor can mean a child knows someone at school always has his back (and that someone is not necessarily his teacher, who must discipline him at times or correct him.)