When you buy suits, buy all the pieces you might wear: Jacket, skirt, dress, pants. If you have 5 such suits that is plenty. I'd say 2 dark grey, 2 blue, one black if you need black. If you work in a less formal environment or warmer weather city maybe replace the black and one grey with a tan and light grey. I find bottoms like the skirt and pants wear out faster than jackets, so this way you won't wear out your skirt/pants as fast since they get worn 1/3 as often.
Then, I'd add at least 2 more bottoms and at least 2 blazers in tweed, a solid color, or a pattern. Make sure the jackets match at least two bottoms. For me, these are jackets that don't reveal much of the shirt underneath, and all go with black.
Then, I think you need at least 6 tops per season. I think these should all be tops that you are comfortable wearing without the jacket, and a few extras that might be just under a jacket. For me, this is 6 warm sweaters (winter), 6 light sweaters (fall and spring), 6 short sleeve blouses (late spring, summer, and fall), and 3 dressy t-shirts. My preference is that every top go with every suit, but if it goes with just 2 suits that would work too. And, if you have the suit dresses, remember that they are also tops. In LA, you might go with 8 average day shirts, 6 hot day shirts, and 4 "cold" day shirts. Mine are all solid, but I think one of each heavily patterned would be fine, and maybe or 3 with a smaller or more subtle pattern.
Why 6 instead of 5 and why blazers that aren't part of a "suit"? The jackets are memorable compared to the suit so you wear one or 2 a week and don't repeat the next week. You don't want to wear the same thing every Monday etc. With 6 tops plus at least 1 jacket a week you won't fall into that. So: Monday- Suit 1, top 1, Tuesday Jacket, Wednesday Suit 2 with skirt, top 2, Thursday Suit 3, Top 3, Friday, Suit 4 top 4, Monday Suit 5, top 5, Tuesday Suit 1 with dress, Wednesday, Jacket #2, Thursday Suit 2 with pants, top 1, Friday Suit 3, top 2 with alternate bottom and onward.
I'm a fan of Talbots for quality plus size suits, and also Jones New York, whose suits are washable! Both have pretty good sales here and there. I also have several Nordstrom suits from the house brand that I found on the clearance rack. I search Talbots, overstock, and 6pm for the blazers at reduced prices, and sometimes get lucky at Macy's or weirdly, Coldwater Creek. Black pants can be from wherever.
I don't really accessorize, because I hate feeling jewelry on my body. You won't be the office fashionista, but you'll look fine.