Should I have signle jsconfing.json and eslintrc.json in sfdx project that is in fact monorepo or I need separate configurations for each directory/package? What are pros and cons of mentioned approaches?
By default, the CLI places these files in each LWC folder, but this isn't necessary; the validators will walk up the file path until it finds files by those names. Unless you plan on using those engines for Aura as well, you might want to keep a file in each LWC directory. You'll get slightly better validation performance, but it's very marginal performance-wise.