Any of those should be acceptable. Your meaning will be understood. The rules of grammar have been relaxed greatly from what they were 50 years ago, especially with grammar "correction" software which wants to change my "I ate an apple." to "I ate and apple."

I would avoid frontend as it takes a bit longer to parse. It makes perfect sense to me for someone to write:

I am working on the front end of this process and need to hire some front-end developers.