I'm not sure how to answer the question "what are the basics of good template design" because that's a very broad subject. There are many websites that offer tips about how to utilise screen real estate, how to use white space, fonts, colours images, as well as offering helpful warnings about things you should not do (like overusing animated images, colours that cause eye-strain or that may trigger neurological reactions - like epilepsy) and you could spend hours (or days) learning from what other people have done.
As far as
Kunena is concerned, the "basics" of template modification are not that difficult to learn (particularly if you have any understanding of HTML and CSS) as the tutorial in the documentation Wiki gives a few hints about:
Changing Template and its Colours - the Basics
. This is something that, I think, every novice user of
Kunena should be aware of.
Learning how to develop good web presentation, though the use of Cascading Style Sheets (CSS), is a skill that will benefit you forever. Using web stylesheet analysis and development tools, like
Firebug for
Firefox, is something that will repay your investement of time a thousand-fold.
However, as you say (and I'm pleased that you have said it) concentrate first on getting your forum up and running and then you will be in a position to consider how you might want to change its look or even whether you should!