PPI=DPI for most purposes. If you want it sharp and crisp, render bigger. (Understandably it’s going to be a pain because it takes longer. But can’t be avoided.) Setting DPI in file output usually works for printing from most image viewers. However most 2D software for editing ignores that or lets you set differently. In which case up or down scaling is what really affects the DPI density, so you’re likely better off rendering bigger than you need it.
In regards to Inkscape text being sharp, it’s because of how vectors scale up or down. Render outputs on the other hand are bitmap, so again with the whole making it big so there’s enough there to make it crisp rather than pixely.
BTW, if you’re doing it for print/publication, I’d suggest using Scribus to lay everthing out. Nice bit of FOSS for desktop publishing. Not quite InDesign, but imo it’s better than Quark. Grids, flows, layouts, does it all nicely. You can print directly from that program, but outputs to .PDF so you’re fairly well set if wanting it printed by pros. Of course like any capable software, there’s a bit of a learning curve - particularly if new to DTP.