I am not a BI, but will discuss what I have learned in the past three years about Secret and Top Secret clearnaces.
1. Be prepared for a long wait period. My Secret clearance took almost 365 days and I wasn't even interviewed. Gaining a TS was shorter, closer to 225 days from filling out the SF 86 throuh adjudication. No interim was given. I have other colleagues however who are going on day 365 and have yet to be contacted by an agent for their TS interview.
2. You are a U.S. natural-born citizen. You will declare on your SF 86 your parents nationality. You'd better ask your father if your mother was a U.S. citizen or not if you still have no contact with her. You will also need to disclose any other foreign contacts. Be honest and list them. Having foreign family or friends may not in and of itself be a disqualifying factor.
3. Traveling outside the country may not prohibit you from getting a clearance. It all depends on where you go and how often. You will state on your SF 86 travel to a foreign country in the past 7 years. I have traveled to various Caribbean countries over the past 7 years on vacations and it wasn't a big deal. During the interview I was asked about it and explained it was for vacation purposes. There will be follow-on questions but from what you stated it won't be a problem.
4. Getting fired from a job by itself may not prohibit you from getting a clearance. Your friend must have stolen something or had other character issues that came about during the investigation.
The best piece of advice I can tell you is this: Telling the truth will never make you forget who you told what.