Not overstock, but you might have some aggression with the bottom dwelling fish. (The gobys and the jawfish)
Do you have a picture of the tank? What is the tanks length?
(also keep in mind that mandarin gobys are very hard to care for - are you currently growing pods to feed it?)
I agree with this. I would ditch the jawfish and Blenny and just go with Goby's.
Blenneys in theory are peaceful fish. In my experience they really hate Goby's. I had a small Goby and a Blenny in a 100G reef and had to remove the Goby as the Blenny chased it constantly.
Mandarins are not Goby's (despite often being labelled as such). They are Dragonets. They will very rarely eat any food you will give them and are completely reliant on your tanks population of pods to survive.
In a tank this size, assuming adequate amount of liverock, you will probably be ok. Just make sure that the rock is mature with a strong population of pods and be ready to supplement it. Again in my 100G tank I kept a Mandarin just fine, however I was lucky enough that mine would eat some frozen food as well and I also cultured pods and had a refugium connected to the tank to make sure the pod population was always high.
Purple Tangs are probably not a good idea to have in with yellow tangs. They are very likely to fight.
Blue tangs and Yellow tangs "might" be ok together in a tank this size but personally I'm not sure I would risk it. If It was me I would skip the yellow tangs and just get the blue tang (depending on your tank dimensions, they need a LOT of swim room and very good water flow). Blue tangs are one of my personal favorite fish though and I have never had a tank big enough to keep them so I'm slightly biased...
If you are going tangs definitely get yourself a good quality UV filter. They are absolute nightmares for whitespot. Once they are settled and assuming everything is ok its not so bad but I kind of consider a UV filter to be an essential for keeping tangs.
Engineer Gobys - I haven't kept them myself but if you have them make sure your liverock is super secure. Put down some egg create and cable tie your bottom layers of liverock to it. Use marine putty and/or drilled holes and acrylic rod to keep the rock held together. You also need to have a good deep sandbed with a mix of fine to course sand along with rock rubble, etc. These guys can move a MASSIVE amount of material and can very easily cause rock falls if your not careful. Like tangs they are very prone to whitespot so get a UV filter.
One more note for engineer goby's, again they are not actually a goby, they are their own separate species. They are carnivorous and will quite happily eat anything that is small enough to fit in their mouths (possibly real gobys may be small enough).
I'm not seeing any major issues with the rest but I have been out of the hobby for awhile and my knowledge is a little rusty so don't 100% take my word for it.
One suggestion I would give is maybe ditching the tangs and looking at wrasse. There is a lot of different types and generally they are mostly peaceful and easier to keep than tangs.
If you do go for tangs maybe look at getting some macro algae growing in the tank. I honestly don't know how long it will last in a tank with tangs but is something I have always wanted to try.
