Hey man, I have two guitars which I have tuned down really low, one in drop b(dropped d, then everything down one and a half steps) and the other just have everything down one and a half steps...the one guitar in B is a Baritone, so that works well, if you can try and get an Ibanez MMM1, I love mine,its amazing!
Then the other guitar is a Cort s2550, with a floating Wilkinson trem. For that guitar, I had to put another spring on the trem unit, so as to stop the heavy gauge strings from pulling the bridge up to a 90degree angle with the body...that is relatively simple...just add a spring, then tighten the two internal screws that pull those springs, untill the bridge is at a comfortable angle...this process is quick...about an hour or so, but it needs to be refined after tuning your guitar....then just stick on some heavy strings...dont worry about a 7string set, just get some 12's, they are heavy enough, I use Zakk Wylde signiture Ghs Boomers on my Cort...they are 10-60's, so really nice for the high strings, and heavy as **** on the bottom!
But, it isnt good for your guitars neck to downtune hectically, then put it back into E, I would leave it downtuned to c-sharp...good luck man...ideally you would want atleast two guitars if you want to play in a variety of tunings....I spend almost all my cash on guitars...and I am now getting to the point where I have more that I have one guitar in every tuning in which I play....so does anyone have any suggestions for weird tunings? maybe some open chord tunings...as I am starting to mess about with a slide, but of course it sounds pants at the moment! any weird tuning ideas? for metal/industrial vibed stuff