Relays or MOSFET could be a good choice to drive the igniter. Look at your local part supplier if you could find some overstock relay. I found some in here 10Amp rated, 5V coils for less than 2$.

32 outputs... why not. Many 40Pins device gives you 33 i/o. 1 left for the audio input... just perfect. OR, using a smaller one with an i/o expander... in this case you don't just add extra part... but also a little bit of delay... but few ms will never ruine the show. In another hand, if one day you decide to add other outputs, you just need to add extra i/o expander.

Let's say a PCF8574, give you 8 i/o and you can use 8 of them on the same I2C bus... 64 outputs.. not bad.

A pic 12F would do the job, leaving few i/o for audio and stuff.