Map out your future 1-7 yr resumes staying at your current job or going to a regional airline. I'd use a 3, 4, or 5 year upgrade at the regional. Minimum of one new type rating and hopefully 2. Don't sit on one plane, learn something new if you can bid a second aircraft and not delay your upgrade. Compare and contrast the resumes. 3,000 hrs of 747 SIC, with few landings, isn't going to improve your abilities as much as you current resume and 500-1000 hrs Part 121 TPIC in X years.

I'd give myself maybe 300 hrs the first year at the regional? Onboarding time, training, IOE, reserve, etc would keep you TT down. After that I'd guess 800 hrs, if not more, might be achievable? You know what your current company's upgrade and yearly flying hours is like.

Good luck.