I've only just arrived in D4 as well, but your arena does look a bit undersized. I think you should add bleachers. Although they're the cheapest per seat, and most volatile, you'll make most of your arena money off bleachers.
How'd you estimate 28K per week? Because this week shows TV contracts from your previous league. That should increase by ~10-15K already (at least it did for mine). To calculate it more directly, find the player salary floor value and divide by 0.8.
Staff salaries at just 17K sounds like you're scrimping. Are you training? If so you'd be better off getting a higher level trainer (go for 4). Doctor and PR man can be scrimped on I suppose. I've used a level 3 doctor my whole time in BB, and had I think 3 injuries that lasted more than the game they occurred in. I'm using a level 4 PR man, mostly because when I went up to level 4, I found that the overall fan survey took a lesser hit when one of the categories went down.
For whether the guy is capped, try JosefKa's formula. I would sorta think star potential could be higher than 25K, but salary is a poor indicator. Plus, a low sublevel of star potential might be in that range.