It doesn't have to be 1:1 personal redundancy -- it's more like, several of the 20 devs being able to assume lightweight PM/DS/DBA responsibilities for a few we

It doesn't have to be 1:1 personal redundancy -- it's more like, several of the 20 devs being able to assume lightweight PM/DS/DBA responsibilities for a few weeks while that person is away (I've personally as a dev covered for pretty much that set of roles -- and always had a renewed appreciation for the skills of that person when they returned). In other words, don't silo your roles too rigidly, especially when you're small and can't afford 1:1 redundancies. And if your company absolutely 100% relies on having a full-blown PM/DS/DBA around at all times, well, then you DO need (at least) two of each, otherwise your company tanks if your one DBA gets sick or leaves for a company where they don't have to suffer the permanent stress of being a SPOF. And if you CAN survive for a few weeks while you hire and train a new DBA in that situation, then you can survive for a few weeks while your DBA is on holiday.