I wish I could answer your questions, but I have really no idea:) Anyway, good luck with the tournament!
How to design PAIRING CARDS?

3 rounds will potentially give a clear winner with 8 players. 4 rounds for 16 players. If you only go 3 rounds with 10-12 players you will possibly end up with two players with perfect scores.
2^n = max number of players to only have one perfect score where n is the number of rounds. So a 5 round event will only allow one perfect score with 32 players.
As to a pairing program for your smartphone, I've never looked so can't suggest anything. With only 10-12 players you should be able to do it manually without much effort, if you know the pairing rules fairly well; tie-breaks will be more time consuming though.
Greetings to all, it’s been a long time that I want to post here but couldn’t manage because of a very poor schedule. I am expecting to organize a very short 1day chess tournament of around 10-12 players on Swiss basis. How many rounds should it be? & how can I establish a pairing card, after assigning an ideal local rating to the opponents on the basis of their strength. I have used basic version of Swiss gravy on my Smartphone but it often miss the progress so I had to go back and re-enter from the first round which is very exhausting & Swiss Champion which was good but with a 10 players restriction. Obviously it looks very silly in this modern age where we have softwares to our assistance, but I really want to know is their a systematic way to manually evaluate pairings &tie-breaks with alternate colors, that is close to perfection and what must be an ideal time for a match? We would have almost 8 hours on day. With so many gentlemen at site I'm hoping this time i would get a solution on my 5x2.5" screen.