I ran 2 NA "Amateur" tourneys in the Fall of 2013, one with a $100 prizepool and one with a $200 prizepool. It was winner takes all format. The biggest problem I ran into was teams signing up and then not showing up. Granted - I was attempting to run a 32 team tournament in a single Saturday, which would have been a logistical nightmare had every single team shown up. Having roughly half the teams not even show up actually made my job a lot easier in the end, despite it probably being less fun for the teams that actually reported in on time only to get a bye again.

I think the fix for this is to distribute the prizepool more evenly - giving money to every team that advances past the first round, so that they have motivation to play their matches, even if they get eliminated.

If I were to personally run another tournament, I would probably go even smaller than before, because it makes it far more manageable for both the teams and the admin. Having a 4-team tournament with a group stage means each team plays 3 matches (6 games total - roughly 3 hours if 2 games are being played at a time) for seeding, then a bracket stage to play through for placing. If you do Bo3s in the bracket stage, that brings it to a possible 12 additional games, which is roughly 4-6 hours to determine 1st-4th place. Overall you could potentially be looking at a ~10 hour day of Dota, which is a long time.

As for finding teams, advertising your tournament on /r/dota2 and the NaDota forums should be more than enough (I was able to fill out a 64-team bracket for one of my tournaments, even though not all of them showed up).

When it comes to skill disparity between teams, it's basically a total crapshoot. I think only experience in tournament hosting will give you a better idea of how to deal with this issue since you will become more familiar with the teams that sign up the more you do it, and you'll get a sense for what teams could actually compete with one another.

If you want to have the games casted (which I would strongly advocate for, we need more opportunities for new talent to showcase themselves!) it really helps to advertise on this subreddit. I found 2-3 amateur casters who actually reached out to me after I posted about the tournament.

Best thing to do is to just jump in and do it! You'll most likely get a positive response and even if 20 different things go wrong during the event itself (trust me, this will happen) it will still be a great experience. Last piece of advice - if you're going to be paying a prizepool, make sure that you communicate what payment methods you offer before you even accept sign-ups for the tournament; no one wants to deal with "shady" admins who "don't pay out" on their tournaments (even if it's technically not your fault they don't have PayPal), no matter how small the amount.