Dom

Cymbals (including hi-hat) and the snare drum are what I'd improve first. They make the most prevalent sound and are likely to be played the most so having them sound good is a good bonus. I would definately not reccomend starting by getting a china and double-bass pedal. A china cymbal isn't used very often in comparison to other things and you definately need to learn the basics of one bass pedal before you even think of moving on to two. New, more durable heads (such as ambassador coated) are also another thing you should upgrade fairly quickly, although it's fine to wait until your current heads break before replacing them. I would also suggest you learn how to tune drums straight away as tuning can make a huge difference in how the kit feels to play and how it sounds.

If you're on a low budget, upgrade the snare first and then the cymbals (either individually or as a set) and then move on to whatever you feel like needs improving the most (probably toms, as a good tom drum sounds awesome).

As for songs, well, most songs out there can either be played straight onto or be adapted for a 5-piece kit.

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