Foremost, if that TKD school is Olympic style, I would split. They'll be training for competition, but points-based competition. You'll find no good sparring partners there. If they're a very legit TKD school, see below.
I would either do TKD or Muay Thai, not both. Two different styles that have the same or at least similar goals. If it's a good TKD place, they'll still show ya elbows and probably knees. And obviously, they both use fists and feet/shins. However, they are two very different styles. In arts like TKD or kung fu we use our feet/shins as if they're a knife, wanting speed and perfect accuracy, and hitting the most vulnerable targets at the best opportunities. Muay Thai or karate use kicks like a baseball bat, swing that thing hard as hell, and no matter what it hits, it's goin' to hurt it. If you're just training for MMA, I'd just go for Muay Thai, as much as I hate to be cliche. It'll help you jump into the sport far quicker than TKD will. You have to understand that even a legit TKD place is going to be having you do forms, very possibly be conditioning you for self defense, and they'll be teaching you things that just aren't as applicable for sport.
I'd drop the boxing. Save that for later. Focus on Muay Thai (or TKD). With all the stuff you're doing, no point in paying gyms fees at one more place just to get in maybe one training session there a week. More importantly, Muay Thai will generally offer you all of the same punches, but just won't have the same focus. You're just better off hitting the Muay Thai school up for another session, or working your stuff at home, or even just taking a day to rest.
Basically I feel the same about the Sambo idea as I do about boxing. You're already looking at two ground arts, and probably three+ arts in general. Do you really want to pay another gym fee for one or two sessions a week at the Sambo place? I'm not saying there's actually anything wrong with taking Sambo, but you should drop either the wrestling or BJJ if you're going to put the Sambo in there.
Just seems like you're spreading yourself too thin being at so many places.