Most of the problems should be corrected in the mixing process. Mastering, on the other hand, is designed to address subtle EQ imbalances.  A mastering engineer can provide a stronger balance throughout the composition and reduce sharp transients, but everything else has to be dealt with earlier. If you need to find an engineer to help you, I advise you to go to https://majormixing.com/ , I've used their services more than once.