1) B is 0.01uF,50V,+80%,-20% axial ceramic capacitor.
2) I believe your statement is true. The +/- are the tolerance ratings.
3) Do NOT confuse the "SR" with the "SRC" components. SR are network resistors. SRC are network resistors with capacitor. SRC components are no longer manufactured but you can leave off the capacitor component and use 9-pin,8R network resistors. See http://www.pinwiki.com/wiki/index.php?title=Williams_System_9_-_11#Repairing_Alkaline_Corrosion for more details on this.
4) Yes. A 6821 is a 6821. Does not matter what company manufactures it.
5) Those letters are usually codes for certain things. There are sometime letters between the numbers (e.g. 7402 vs 74HC02 vs 74HCT02 vs 74LS02) and those may make a difference.
Good luck with your repair. I would advise you check your traces before putting any component back on the board as it's easier to see and fix the traces without components on the board. You also do not want to unnecessarily undo any work you have done. Most of all ... enjoy the ride. It's often a LOT of work but when it finally works it's satisfying to bring a board back from the dead.