Nissan Micra Engine Problems

Are you talking about the cam belt, or the belt driving the alternator, water pump and other accessories? If you are talking about the latter it would usually only be changed if it was clearly worn when checked visually. If you're asking about the cam belt, the Micra has a chain, not a belt, so it doesn't need changing regularly. The only reason you might change it was if it was noisy and loose, when there's a risk that it could jump a tooth and damage the engine.

Putting the blankets over the engine and bonnet means the engine doesn't cool as much while sitting overnight, so isn't as cold when you come to start it in the morning. I'd say you need a new battery, one with good cold cranking power, as I reckon the drain on the battery as it tries to turn the engine over is too high and the engine isn't getting enough power to start. Once it fires it's fine, that's because it's then not having to power the starter.