Is it advisable for our photographer to do the formals in medium format and the candids in 35mm?
This depends on the methodology and philosophy of your photographer. Many contemporary photographers employ the mix of formats using the advantages of each. Let your eyes judge the merits. What is the best way to get a mix of black-and-white photographs along with color — assuming that’s possible? If using the B&W just for the newspaper, then ask for a Panalure (b&w) or glossy color print. If you want some b&w for their artistic merits, your can either have some images originated in b&w film, or have it all shot in color and decide later which ones are best for monochrome treatment. Some professional labs now offer Kodak Ektamax prints forb&w images from color negatives. Advantage is that you get a nice print, while avoiding the logistical hassle of having two film types shot which complicates the photography and increases chance of a mistake. But Ektamax is really a color paper with B&W dyes. If you are asking for B&W for its archival properties, or want substantial B&W coverage, get
