Book translation from UK English into (Brazilian)Portuguese

I have a teenage novel of 86,000 words that I wish to have translated. The vocabulary includes a few less-common sailing terms and a few simple scientific terms. I need this translating, with good punctuation and paragraphing the same as the original. Payment will be delayed whilst the translation is checked by a bi-lingual proofreader, who will be working on my behalf. And whilst I would not penalise you for a small amount of proofreading mistakes, I would withhold payment if the translation were not of a good quality that reflects the original story.