OP, you'll be fine. The imms are very flexible on what is a permissible focus. I've played foci ranging from "found a powerful clan of assassins" to "climb in social status" to "grow the best garden" to "repay the debt you owe your family."
But here's my advice for people new to dwarves:
First, make your focus something you don't need to keep secret and can wear on your sleeve. It's better for getting into the dwarven mindset if your focus roleplay can be external and visible. Save the secret evil foci like "kill all the humans" for later when you trust yourself not only with dwarven roleplay, but with lots of isolated, solo and internal RP.
Second, make your focus concrete but subjective. By this I mean it's something you can make small, concrete steps towards the goal while having your dwarf continually dream up more and more fanciful, complicated and difficult things to do as you go. For example, say your focus is to have the best, perfect collection of knives. Because "collect knives" is a fairly concrete thing that is well represented by game mechanics, it's easy to make regular, explicit progress. Oh, my dwarf acquired a new dagger. Progress. Hey, I met a craftsman who makes unique knives. Progress. Nice, I can finally afford a safe place to store my gigantic knife collection. Progress.
But because the "best collection of knives" is subjective, there is actually room for dynamism and growth as your dwarf's view of the "perfect knife collection" gradually shifts from "I'll just pick up every dagger I find" to "I now see only perfect daggers are worthy of my collection--time to abandon my apartment filled with cheap rinthi daggers" to "The best collection of knives will be solely of unique knives with important histories--and I can acquire my first by commissioning a custom knife made from templar femur and using it to kill a Sorcerer."
In other words, the focus is actually achievable, but you reserve the right to decide when and how the focus is achieved. This gives you a way to always have small, real things to do to make progress towards the focus while preserving control and flexibility over the character's arc.