Can you combine any number of figures of speech into a single one? By that, I mean can you combine as many as you want into one. Let's say you want to use a metaphor and then combine it with irony, or an allegory, an irony and a hyperbole at the same time, can you do that? What are some of the most complex figure of speech combinations we can use?
Kind of, but don't go overboard.
In theory, yes, you could combine as many literary techniques and figures of speech together as you want and it would make for a semi-coherent piece of writing. However, it wouldn't necessarily be very good writing, and a lot of the deliberate meaning of literary techniques is lost when they are smashed together like Play-Doh.
The nonsensical usage or combination of unrelated words, literary techniques, etc. is most commonly referred to as catachresis, and it usually comes across as eccentric and out of place to the reader. It has a subtype called abusio, which results from combining two unrelated metaphors ("We'll cross that bridge once we open that can of worms."). Abusio is usually for comedic effect, but catachresis requires a more delicate touch. The main effect of carelessly using catachresis is that your writing comes across as extremely exaggerated and strained at best, and written by somebody who is not very proficient in English at worst.
Catachresis is a figure of speech in which writers use mixed metaphors in an inappropriate way, to create rhetorical effect. Often, it is used intentionally to create a unique expression.
Furthermore, according to Wikipedia:
Catachresis... is the name given to many different types of figures of speech in which a word or phrase is being applied in a way that significantly departs from conventional (or traditional) usage... Catachresis is often used to convey extreme emotion or alienation. It is prominent in baroque literature and, more recently, in dadaist and surrealist literature.
When used with clear authorial intent, the effect is usually intended to come across as weird and out of place, for a specific literary purpose, i.e. a character who deliberately misuses figures of speech for humorous effect. It gives your writing a unique and Dadaist feel, like something written deliberately as counterculture or outsider art. That may be exactly what you were going for - in which case, go for it - but if it's not your intent, all it will do is confuse the reader and make them unsure what you're trying to convey.
When used correctly, catachresis can be very funny. When used incorrectly, it sounds like this:
Her laughing feet fell overboard with amusement.
Which makes no sense at all.
Thus, unless you have a specific authorial purpose for creating catachresis in your writing and you fully understand how to apply it with the proper care, just don't do it. It's too confusing and easy to get wrong.