If you're shooting portraits in a controlled environment like a studio, MF shouldn't be too big of a deal.
Now looking at $90 difference to lose 1/3 of a stop and gain USM focus for the canon 85 1.8 is probably worth the money if you plan to shoot outdoors.
If you're bouncing around different lenses and focal lengths, stop for a few minutes and use your 18-200 to figure out what length you like best. There's a big difference between positioning, perspective, and style between a 30mm (28, 35 included), a 50mm, and 85mm. Once you pick the range that fits you the best, then start deciding on a lens and what you need.
Don't worry about effective focal lengths right now. You're not gaining length, you're adding more pixel concentration to a smaller area than FF at a said focal length which gives the appearance of more length when viewed at 100% side by side.
T3i, Sigma 10-20, Sigma 30 1.4, 18-55 kit, 55-250, YN-565, a few books, some software, and a desire to get good.....