Hello and welcome!
You have received some good advice here already. @NickLowe linked to a useful discussion. I will add this one, with some more updated workflows: Using DEVONthink for Literary studies. Round Two.
There are also these brilliant resources:
- DEVONtechnologies | Handbooks and Extras
- Take Control of DevonTHINK (at the same link)
- and in case you are inclined to spend some money and like a good course, see DEVONthink Field Guide | MacSparky Field Guides.
A lot depends on your DT and MacOS literacy. I am a longtime user who has never started with scripting; but there are some brilliantly gifted users online here who get a lot of mileage out of automation and customisations. These things may quickly overwhelm.
So I would say you don’t need to start big. Start small: create one database, make an informed decision about indexing versus importing, add some resources, really think about what workflow would suit your academic practice. Think about what sort of resources you collect, and what you need to get out of them; how often; in what formats. Read the manual a lot, and press all the buttons (well, most of them…) It’s really hard, if not impossible, to build a system around all of your current and future needs from scratch. Rather, let DT grow around you as your needs become more varied and more demanding over time.
Have fun, too 
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And let us know what you are working on. Always good to meet a fellow academic user, and there are many here on the forum.