How much theory should be given in article? I have created a software and the assisting methodology for its application to some kinetic studies. I used a lot of theory. E.g., I used kinetic model, reactor model, data analysis (about 7 methods to analyse the results totally). Now I have prepared an article where I report this methodology and demonstrate the results of its application.

How much theory should I include into the article? Can I only refer to other publications/books for the models/methods proposed earlier?

I have seen many publications where a part of theory is taken out from the main text to appendices (example with 5 appendices). In some journals appendices are not included into the article (supplementary, accessible online-only). Is it a good solution to include some theory in appendices? If yes, how many appendices would be OK (i.e., would the reader like the article with 7 appendices? As for me, I do not have anything against many appendices).
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.