1991 745 Turbo Auto

I have a leaking exhaust manifold near the first second and second cylinder. I have already read the 700/900 FAQ regarding how to fix this problemm as well as doing a Post Posting research. I feel a rush of air from under the exhaust manifold near the front of the engine each time I rev up the engine. I already tried to button down the nuts near the leak and it did not help the situation.

The FAQ and almost all the researched posting warns you to watch for and even expect to have broken exhaust studs when replacing the exhaust manifold gasket. If this occur you have to tap & die the stud out or take the head out and have a machine shop do it depending on which stud get broken.

My question are:
1. What are some of the negative effects if any of not fixing this problem right away?

2. Would a decrease in gas mileage be one of these effects? The reason I ask this second questions is that I noticed a definite decrease in gas mileage starting two months ago, (the same time I found the exhaust manifold leak.) I was getting 22 mpg in mix city and highway driving and now only get 16-17 mpg.
3. What are some other hints besides spraying all applicable studs and nuts with PB Blaster each day for several days before starting this project?

4. I am hesitate on starting this project because I don't have the time or money to pull the head and get a machine shop to fix my problem if I do get broken studs.

I thank everyone in advance for their response and advice regarding my posting.