Just to be honest with you, I believe expanding the arena drastically right now in anticipation for the move up is over-rated. With what other Div. IV teams are getting for seats, it takes two full seasons of home games to just get back the money you spent on each seat. You pay $200 to build one bleacher seat, and then you sell it for about $10 or $11, meaning it takes you 20 home games before you start to see a profit for that seat. And with 11 home games per season, that's nearly two full seasons.
Now, I fully understand that long-term, it's a completely different story and the seats are invaluable long-term. But for the next season or two I don't know that expanding the arena in a major way will be a priority. I think I'm going to take the best of the best of my team and add a couple of stud players (stud for the league I am in) and try to win again in Season 19. I understand that won't be easy, and I understand that I'd be crazy to expect to repeat the 20-2 I've went this current season. But I fully expect to compete with the best in my league next season and make the playoffs with a chance at making a deep run in the playoffs.
Sorry but I think this is a terrible thought process. I don't think there's anything more important to spend money on in this game than your arena, especially if you're about to move up a level. It's your biggest investment and the most important way to bring in long term income. Ignore it and all you're doing is stagnating your team.
Suggesting to spend that extra money on 'studs' makes it doublely worse because you've just just greatly increased your team's weekly expenses (wages) instead of increasing income (arena revenue). And that effect doesn't just effect your team one week, it lowers your income every subsequent week as well.