First, WELCOME to RIU. You will find a lot of great information on here, but also some not so great information. The most important thing is to continue to learn and do individual research to find what works best for you in your garden. Make use of the forums search bar, as this is a great way to find threads that are posted on topics and questions you may have. Furthermore, don't take information as being a 100% valid without verification, I prefer members who have photos, videos, etc to back there claims, but even then every garden and grower are different.
Finally, please know that "Well-Known Member" doesn't necessarily equal "Great/Knowledgable Grower" as many new members tend to make this assumption. I am a prime example of a new grower, who has received this status simply because of my activity on the forum!
Best of lucky with all your grows and again welcome to the RIU community!
Second, I would have to agree with the above post on getting an extraction fan to try and cool the closet a little bit as 90 is high unless running co2. I noticed early on that my 600w MH was too much for my little seedlings to handle, which is why I have gone to T8s in my veg room, however I am kicking myself in the butt for not going with T5's instead. Once the plants have matured however, this is assuming you get the temps under control, I have ran my 600w roughly 12" above the canopy and the plants seemed to love it. Just my experience though, and every grow is different.
Again, welcome to RIU!