Wow, lots of questions, here we go:
Expect 50 games a week in HD. They will use any HD feed they have available on the satellite (in general). Most teams are doing home games in HD. Some teams are doing all games in HD. So, in general, DirecTV should have MOST games in HD (using the home feed, or occasionally the away feed if needed).
The HD games will be on a -1 channel, like it has been for NBA & NHL this season.
Blackouts will be the same as last year.
FOX Saturday afternoon will have one game on locally, but televises 3 games nationally. You'll only be able to see the one on you local station. No Extra Innings games can be shown until 7pm Saturday. So when a team scheduels a 1pm game, it can only be seen the the home area. (Eastern Times)
ESPN sunday night blackout is just for the one ESPN sunday night game. No other games are generally scheduled during this time (start after 7pm Sunday nights)
Also, you will be blacked out of any teams that are considered your home area. For some people that is one team, for some it is up to 5.
Check this site to see what teams are considered your home teams:
Local Regional Sports Network Information
All teams listed on that screen will be blacked out. You must watch the home broadcast using the OTA/RSN in your area. If it is on a local network you don't get, you are out of luck for that game.
Lastly, they are aggressively working to provide dual feeds (home & away) for this year. I've asked the powers-to-be about it, and they wouldn't confirm it, but said they are close.
They did it very successfully with the NHL this year, which has far less HD feeds, so this could be a very good year for the MLB package.