I really like the concept of this, and it would most certainly make the game more realistic. For number 2 and 3 I'd say go for it.
I have a bit mixed feeling about number 1, and see both upsides and downsides. It would be very fun, to be forced to plan ahead at preseason, and then adjust at AS-break with a couple of final additions.
Upsides: It would probably lower the inflation that has hit us. Yes the demand would be huge, since every team would be looking to buy players in the short off-season. However, the supply would be accordingly larger, since every manager would also be looking to sell players in this timespan. It would take away the ability to list a player at a crazy price and then just relist him over and over again until someone finally bites.
Also it would give the BB's a better chance to manage the market prices, since they could unretire a number of players, matching the demand there is. This way they could even out supply and demand and achieve a fair market equilibrium.
Downsides: It would make it harder to keep new users than it already is, since they would be stuck with a team full of trash players. Personally, if I signed up and found out I had to wait more than a month before I could make any real change to my roster, I probably wouldn't stick around. This would also take away the option to train a few players, since the team you start with only have one somewhat trainable player. In order to counter this, new teams would have to be awarded at least 3 quality trainees, and even then you wouldn't have the ability to add any players that can make an in-game impact