By the time you promote, your arena should definitely be around 7000 seats. When you promote, your fans will flock to your arena. I recommend building lucratively until then and setting your prices a little high to reap the maximum benefits. I sold out every game until the allstar break. Don't worry about players until your a little ways into your first season in D. IV and know what works and what doesn't in D IV. Also Manage GS and ENTH if you aren't already.