So I decided I'm going to purchase my first 7-string in the near future and I decided I'm going to tune my 6-string down 3 half steps just so I can use it just for BTBAM songs.

Will I have to make any truss rod and/or bridge adjustments?
Any other precautions?

Am I just overreacting?

It's an Ibanez RG321mh strung with 11s.
11s will be a bit floppy. Realistically you can get away with doing nothing but if your planning on keeping it in there tuning (which i'm pretty sure you'll have to since there stuff requires a lot of time) adjusting the truss rod and intonation would be a good idea. Another factor to consider is that if you go to a heavier gauge it may not be as important to adjust the truss rod considering your already tuning down and the higher gauge would compensate for some of the tension loss.
Truss rod 'might' need adjusting, and you're definitely going to need to set the intonation for that drastic of a tuning/gauge difference. Be aware that the nut might wear quicker if you're using a string gauge that's a good deal beyond the allotted spaces as well.

Outside of that you should be good.
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