My honest answer? Probably not.
I understand not wanting to miss out on anything - I was in a similar position at the start of my S5 last year and wanted to self-study another higher outside of the five I'd already taken - but I really don't see any reason to put yourself under the strain of seven highers when universities want, at most, five. In fact, I had plenty on my plate last year and probably wouldn't have found the time to self-study another higher, let alone find the motivation to get myself to actually do the work.
Doing so many highers also runs the risk of lowering your grades because you're spreading yourself too thin. Trust me, it's better to have AAAAA or AAAAB than AABBBBC or something similar. I can't imagine universities will see you in a better light for taking more highers than the average person if you've not achieved good grades in them. In my opinion, it would be more valuable to take five highers and dedicate your free time to things you can put in your personal statement rather than take seven and not have doing anything outside of school that shows your interest in the degree you're applying for.
There's also the fact that your opinions will change over the year. I almost guarantee it. This time last year I wouldn't have dreamed of taking ADVH Maths and crashing H Physics. I expected that I would be doing H Geography in S6. Now that I'm actually here I'm doing both of the former and I didn't even consider H Geography when making my choices. Just because you want to do three ADVHs now doesn't mean you will want to do them when it comes to actually making your S6 choices. You may decide you don't like a subject after studying it at higher or find the workload too difficult to carry onto an ADVH level.
Of course, at the end of the day I don't actually know you and I can hardly sway you if this is something you're set on doing. I don't think it's worth it but that's just my two cents on the matter. If you're really going to go for it - and I want to emphasise that I strongly advise against it - then I'd, at the very least, ask that if your grades start to fall you don't hesitate to drop a subject. It's really not worth getting a bad grade over.
Regardless of what you choose, good luck with this year. It's an important one.