How much theory should be given in article?
Besides the already given hints I offer another guideline:

Give as many background as you yourself would have needed to get the idea and method before you have developed it.

In other words:

Write the paper to your former self (before you knew about what you've found out).

If you would have been happy with a paper that described the idea and references a lot to standard, readily available books for the background, then go for that style. If you had found it awkward to work through a paper that has a lot of references to papers/books that are hard to find, then don't do that. Note that different principles can apply at different places in the same paper.

These hint is in some way a simplified form of the general hint

Know your audience!

Oh, and also discuss this with your advisor.