1. Availability - It depends. First of all the official player availability is only available for any player after the end of the NFL season. Once the current leagues get past the 2021 Sandbox season, we are all going to be operating under a lot more uncertainty. Let's say it is October, and your only RB goes down with a season long injury. You need a replacement. We will be in the middle of free agency. There is a risk that you bid on a free agent, win the bid, and he goes down the following week. Having a deep roster will become much more important when we have less info on player availability. The exception will be the final free agency period, after the end of the NFL season, and before simulations start. Then the official player availability should be known -- but most of the premium talent may be off the market by then. In that case, you could find the official player availability by 1. going to the League Roster and finding out what Sandbox team the player is on. 2. Going to the League Standings page and clicking on the team there. It will show you the Player Availability for all the players on that Sandbox team. As others have mentioned PFR can be a good source. If he played in the NFL he will definitely be available in Sandbox. In addition, a player will be available if he was on the game day roster, but just didn't get into the game. It is harder to identify these players, but in general, they aren't great players anyway (since they were healthy but didn't even see the field).

2. Position Tiers - I fixed this issue.

3. Position Flexibility - The gold standard is set by our third party data source. They seem to list the position where the player played the most their snaps. My best advice is to play the players that you would think give you the best chance of winning if you were the coach. If you have 2 pro-bowl left tackles and a pro-bowl RT are you going to bench one of the pro-bowl LTs in favor of an average guard? Use common football sense and it will likely work out for you.