you are correct about the PS players counting against the cap, a few years back I don't believe they did. Last year there was a max of 8 players on the PS, has that changed this season? also the minimum a PS player can earn is 6k per week, and are paid weekly, if signed to an active squad they are guaranteed 3 weeks of pay regardless of if they are only on the squad for one week. Also, a PS player can't go from one PS to another PS, they can go to any team's active roster. as for our top 53, right now our top 51 doesn't include some of our players that will be on the active roster such as Collins. I'm using overthecap.com for the numbers I use. yes dead money, and IR/PUP players count, I figured that was a given lol...
Starting with the 2014 season, the PS limit was increased from 8 to 10 players.
The minimum salary for PS players in 2014 was $6300 per week based on a 17 week season which totals $107,100 total. I have not seen the numbers for 2015.
Yes, if a team wants a PS player from another team they must sign that player to the 53 man roster and pay him for at least 3 weeks.
If a player is cut from one team's PS then he can be signed directly to another team's PS.
I use 1M as an estimate for the 52nd and 53rd players because those players normally have cap hits of about 500K.
Once the final cuts are made, the top 51 number can actually decrease if some higher paid players are cut and replaced by lower paid players; therefore, the in-season number is never exactly the off-season top 51 plus 2 more players.
There are a few other quirkly rules such as the Practice Squad rule for International Players. Teams can add an 11th player to the PS if his citizenship and primary residence are outside of the US. The Cowboys have 1 and possibley 2 players on the 90 man roster that would quality for this spot.
At the same time that the limit was changed from 8 to 10, the eligibility rules were also changed. This resulted in many players being eligible for he PS that previoiusly were not eligible due to either too much time on the PS in the past or too much time being on a 53 man roster.