I don't know if this helps, Seamás, but here's a stab. Don't think about the copula as being conjugated like the other verbs. The other verbs, even the irregular ones, are still very regular. The copula, however, is not. First, the copula has many forms which are the same as verbal particles used in other places (e.g., ní, níor, nach, an, ar), and I would separate the two concepts from one another even though their forms are the same. Also there isn't a "root" which take suffixes -- you have to learn each form independently. So ...
Affirmatives are statements like "it is ...".
Negatives is a negated statements like "it isn't ..."
Affirmative questions are like "is it ...?"
Negative questions like "isn't it ...?"
These in past or conditional would be like:
it was/it would be
it wasn't/it wouldn't be
was it ? / would it be?
wasn't it? / wouldn't it be?
Now conditional clauses are like the one's above but add an "if" to them.
Etc.
The best thing to do is print off Lars' table, and use that when you have a question (in addition to asking here, of course).
http://www.nualeargais.ie/gnag/gram.htm