What grade of titanium, there are several grades some are toxic to the body. You need to know much more than just what it is. Grade 23 Titanium is the best surgical grade out there, then there are the steel grades. 316LVM or British Composition D surgical stainless steel is the next best material. Then you have Bio-plastic or PTFE as options instead of steel or titanium.
in the case of all piercings surgical stainless steel is the best. almost all legalized piercers would carry it. Titanium is better than "surgical" stainless (which is the exact same metal silverware is made from) as it is COMPLETELY biologically inert. They make medical implants from titanium for this reason. The reason piercers tend to use stainless instead of titanium jewelry is titanium is more expensive, which would raise the price of a piercing, and stainless works well.
Most professional body piercing studios carry a good selection of titanium and niobium rings in various colors. I would stay away from junk jewellery stores like Claire's and Ardene's just because of the questionable quality of the material they sell. Rule of thumb if the store doesn't do body piercing don't buy jewellery from them (this applies to online shops as well).
If you mixed titanium with anything, you would then have a titanium mixture.
No one answer to your question. This would depend on the particular alloy of titanium, how it is treated, and the bullet that it is trying to stop. Some very large caliber armor piercing bullets are VERY hard to stop.
Yes you can get it repierced however I would suggest a bent barbell or a navel gem this will avoid external irritation and allow the piercing to be done a bit deeper than the first time around.
By the time you are done you would pay just as much if not more than you would have spent at a professional body piercing studio. Piercing guns are so out dated and the quality of the work just isn't what you should expect, go see a professional body piercer of all your piercing needs.
I would suggest you wait til you are done with the medication for your STD. Peircing anything loads you immune system down and if you are trying to get rid of an STD then piercing should be the last thing you need to worry about.
Slug rounds are infamous for not being good at piercing armor. They may have a high weight, but they fly at a very low speed, meaning they don't have as kich power as you might think. So, with that said, no, a 20mm slug could not punch through titanium.
An AK-47 can put a bullet through a 1/4 inch thick part of titanium, so anything around 2 inches or thicker should stop a bullet, it depends on how powerfull the gun is, but the thicker the titanium the better, if i wanted a sheet of bulletproof titanium i would make it at least 5 inches thick if not 6 inches.
Titanium is a metallic element.
Nose piercing
You can work out right away, my advice would be listen to your body. My naval piercing hardly hurt at all but I still avoided doing crunches and other abdominal exercises for a week or so just because of the slight pain.