Self-pubs (for public consumption) tend to need the same sort of editing to do well, and actually run on the short side. The reason why many publishers won't take on a 700 page debut is because of costs associated with editing the work (never mind production and layout; ink and paper are the least of the expenses associated with a book, so even ebooks are expensive to produce), and on a writer whose work may or may not sell, they're taking a risk. Editing costs for 700 pages would be astronomical; a publisher would take that on if they knew they'd make their money back (and most people who get a deal don't need too much editing because they're proficient at writing a book tailored to an audience), but it's prohibitive for self-publishers to do that.

The reason why this applies when self-publishing is that the writer is taking more of a risk than a publisher (who has bestseller projects to subsidise more niche interest books), and to professionally self-publish - as opposed to shove something out on Amazon and more often than not watch it wither on the vine.

There's a rather naive perception of self-publishing being free money. It still needs the same sort of input as traditional publishing but you take on the risk. It's good for people who enjoy the entrepreneurial buzz, but a doorstopper isn't necessarily the best sell here either.

Op needs to learn how to focus themselves and write for a wider audience. They love long books, but in reality most writers start out with shorter, more focused works and self-publishing isn't the solution here.

This doesn't mean op shouldn't put the book out as a private project for himself and his mates, as they have a realistic idea of their ability. But be careful suggesting self-publishing in these circumstances because it does require thought, skill and investment.