Barbara Hettle and Lisa Davis are 2 former homeschoolers that I know do consulting. However, by far, most homeschoolers do not use consultants (me included) and apply to colleges without professional guidance. You can find all the answers you need on the internet.
What homeschoolers should do is apply with as much information provided as possible. In addition to a transcript, they should have course descriptions of the courses completed, materials used, and how grades were derived; they should have a school profile that describes the methodology and philosophy of the homeschool’s operation; their primary teacher should write a counselor letter describing the student.
Whether or not you should have oodles of outside grades, that is debatable. My kids have all approached high school differently which is why we homeschool–customized educations. I have had kids DE and graduate with numerous 200/300 level courses. I have had a dd who did not want to be confined to a typical outside teacher’s classroom coursework, and we designed all of her courses with the exception of 1 that she took through an outside teacher and 1 DE course she took spring of sr yr (after all apps were completed and acceptances heard before she had a grade.) BUT, the courses she was taking were obviously at a very high level (she took a course on the psychoanalysis/cultural themes of fairy tales and folk lore, read Hugo in French, studied French history in French, etc.) Her test scores reflected her abilities and her ECs were stellar. Her outside teacher affirmed her academic strength.
My current high schooler is not as strong of a student as some of her siblings. She won’t be applying to competitive schools or for competitive scholarships. Her application will be far more basic. She won’t need much more than transcript, course descriptions, and test scores.