Yes,
You should be fine. Sweat is not going to hurt your ink at all. I would give the fresh tattoo a couple of days to start the healing process before you go back to full marathin training. Keep it out of direct sunlight for the same time. Use sunscreen and you should be fine.

Relax, its not that bad!
The tattoo need professional help, but it can still turn out nice and strong.
I would add a graphic (such as a dove, or rose, or heart) to the right ofW the name to balance it out. The lettering needs to be re-lined bolder to clean it up. I would also add a drop shadow to the lettering for artistic reasons.
Wait until this is healed, then get to a real shop for a real touch up!

No worries
You will be fine. Feet are always challenging spots for tattoos. Keep it clean and dry, and wash it frequently. Tattoos are suprisingly hearty. Worry about touch ups when it is totally healed. Your artist should work with you.

A design like you posted will likely cost you $ 400-700 US. (or more)
Plan on a deposit and get to a shop in your area for a consultation.

Tribal plays hell with cover ups. Black ink limits the effectiveness of any color laid on top. A few laser sessions will definitely open the possibilities of what you can do after. Any good artist can re-ink and smooth out your original design work. If you are on a budget, that might be your best option.

Welcome.
These forums are pretty laid back. But there are always some that dont play well with others!

I have always liked big, traditional Japanese style for back pieces.
I think a full on, hardcore, Pirate theme wuld be sweet too.

Pretty much anything you can think of really.:p