I have 3 cats. I started with a male, then a female and then got another male. I found that my first male was far more open to introducing a new cat than my female was. In fact, my female was quite aggressive at first when I brought in the 2nd male. She doesn’t get along well with most other cats initial, but definately not females.
In my family, there is a total of 7 cats; not all in the same household but they have all lived together at one point or another. I have found that the best introductions are between males. This doesn’t mean you wont have issues, but I think males are less aggressive towards each other, as long as they are fixed.
As for the litterboxes, I would say you should start with 2 and if you find that they get comfortable with sharing, then you can take the second one away. I have 2 litterboxes for the 3 cats in my house and they all seem pretty comfortable with sharing.
Any reading you do on introducing a new cat to the home will tell you that you need to introduce them slowly. Keep the new cat in a crate or a kennel and let the "Established" cat check the new one out while he/she is in the crate. Then what I have always done is put the "established" cat into a different room and let the new cat check out the house. Show them the food dish, the litterbox(es), etc. Let the other cat out at a time when you can supervise. I would suggest having a spray bottle in case there is any initial aggression. This has always worked for me.