Dragonkith

1)
The Dragonkith is just some generic dragon assistant that could be any creature with or without any class level. Thanks, descriptive text, for being so resolute on background information! The Dragonkith has a d8 HD, 4 skill ranks per level, full BAB, and good FORT. Prepare yourself for dead levels and the inevitable "this isn't for spellcasters regardless of your 'any class' fluff!"
First level gets NA+1 from dragon type scales and a telepathic plea which is a one way message to you from your now-in-danger dragon friend. The scales slowly increase to +4 at 10th.
Second level sees a poor excuse for more damage in the form of a once per day (miss and lose it) extra 1d6 on a single attack. This slowly scales to +3d6 at 8th.
Third level has Detect Treasure, which has to be the best part! It "works like detect magic" except you locate treasure medium sized and smaller worth 100 GP or more. The class just went from dragon friend to greedy rogue. "Don't bother checking this room guys, nothing here... Incidentally I'm just going to rest for a moment. You go ahead, I'll catch up.." Also at 3 is corresponding energy resistance to the dragon's breath weapon type. It slowly scales from 5 now to 15 at 9th.
Fourth level has telepathic link such that you and your dragon can communicate within one mile and are treated as being familiar with each other's locations. This is good stuff.
Sixth level has you gain a single sorcerer spell up to 3rd level which you must meet the CHA prereq to cast, once per day. There are some good spells to choose from (I tend to get the names of the Sorc only spells mixed up, but I think Wings of Cover is the good one), so one spell is better than no spells.
Lastly, ninth level has share spells such that you can share spells with your dragon buddy. Here come the (arguably) dead levels: 2, 4, 7, 8, 10. They all just get "+numbers." Half the levels don't add
anything new, the capstone is +1 NA, the "Special prereq" is "dragon dies, you lose everything," and you have a spidey sense related to your dragon about to die. The class feels all over the place. It isn't so much a dragon friend as an apathetic dragon coworker. I don't see anything particularly special about the class in terms of dragon power or how the dragon bestows power. It is mostly natural armor and energy resistance with the hope that the dragon bails you out when you realize you don't have useful abilities? At least you have full BAB... 4 / 14

2)
Opportunity costs are a bit harder here, because the flavor text is so kind as to open it to all of everything. With that on the line, yes, this is a bad choice. If you focus on just smashy-smashy types, which this really leans heavily towards, it probably isn't great. You get a little defensive power, and even less offensive power. I won't even try a skill monkey comparison because it really only has one utility spell potential. Even a fighter could do more with its five bonus feats than this. 0/4

3)
The prereqs are low, but the feats are not good. BAB 6 is inevitable. Alertness and Endurance are not great. Knowledge arcana 4 is easy and draconic is also easy. I'll stick with minor. 2/2

Dragonkith 6/20