Did you loosen both camshaft pulley's when replacing belt? Lhc-Focus doesn't release the cam pullys in this write-up, however, not everyone is so lucky and if your timing/tension is slightly out your idle will be effected at the very least. That said your ignition repairs did allow the engine/idle to perform well for at least 5 mins so there may still be a weak point in the ignition system.
One thing to try initially is ressetting the ecu by disconnecting the battery for about 30 mins then re-connect battery and start car up (dont touch the throttle). Allow the engine to sit at idle for about 15 mins.....then if idle eventually settles try driving the car for a few miles. This basically teaches the car new running values. There are several methods of doing this and mine is probably one of many but it is a tried & tested method.