anyone know anything about this new gamertag system

I've done this before, and it's due to their word filter in their gamertag system. Xbox Support can't really do anything about it sadly. With the new gamertag system too, if a gamertag is already in use, the system will slap a discriminator onto it (Example
being Example#1234).

they cant do anything about it unless you know his gamertag u can use the file complain system

when a skill is higher and you level it up, it contributes more to your overall level. With that being said, if you are a high level and level up a high skill it will contribute more to your overall level than if you are a high level and level up a low skill.
So to answer your question it all really depends on your level and the level of your skills.

...and even then, you're still a Spartan that also just so happens to be infected by the Flood.

Elites were confirmed long ago to be NPC's in Halo 4. Nothing has even suggested that Knights will be playable. As Bootstrap said, the only time you get to play as something that isn't a Spartan is in Flood, when you're a Flood form.