Thanks for the 2 replies @Daniel, @Wolfgand so far: I spent quite some time researching (reading various reviews) which RDBMS best suited my needs, and my first choice was Postgres for the reasons given and on account of its well regarded clear documentation.
I need a good rich set of functions to manipulate data, particularly date/time, and read SQLlite, being fast but tiny, was poor on that. Being a novice, I am only going on what I read : although a recent annual survey said MySQL is still the most popular dbms - but its due to inertia from it being at one time, best there was, years before proprietary Oracle got control, and that MySQL is not very 'pure', requiring much application crafting, and so 'locks you in' - precisely the trap I fell into over 20 years ago with Access, and dont want to repeat. Somewhere I did read pg needs strong hardware, so I thought to choose HSQLDB, as that seemed 2nd best after pg in terms of 'clean' & adherance to ANSI standards. I got as far as installing HSQLDB on my Nettop and it appears to run ok. Thinking the DBMS choice sorted I then searched for Design tools and a suitable Forms based GUI, but was surprised to find no suitable clients for HSQLDB !. From a 2009 tutorial/review of MySQL Workbench, it sounded just what I wanted, but was 'dog slow' on 2GHz 4MB laptop, and only worked with MySQL I had already rejected ! (I read LibreOffice Base (at that point v3.4) was a very poor FE compared to the FE integrated into Access, and worse still crashes, corrupting your DB. I also read all the Libre development concentrates on WP & Spreadsheet, not Base, which has hardly changed since Sun owned it if not before. But Base, having drivers for both pg & HSQLDB, is my fallback position for Forms GUI if nothing better around). I belatedly saw HSQLDB not even listed in the recent popularity survey, so that may explain why there is a lack of FE tools for it ?
It is for the above reasons I am revisiting the suitability of pg. As stated my DB App will be single user offline use, small, about 20 tables, and many of those will be just short 'picklists' triggered by Form input for easier-validated dataentry. I notice the FAQ, User Manual, & neither of the 2 replies directly addresses my primary question: "If Atom class nettop not sufficient, would like to know the minimum class of CPU, RAM, GPU required." Is it quite difficult to make even a rough recommendation of minimum hardware for the above 'small' db ?