Want to tune up my Metro

Hey, I have a 95 1.0L (hatchback) Metro and would like to tune it up a bit, but I'm not sure wher to start, I don't want to change my motor (it only has 135 km and I don't have a shit load of money to put in my car). So, what can I change to add some power to my car? I know there's the air filter I can change for pretty cheap, is there anything else?

Thanks

Bosch Platinum +4, or Iridium plugs, new cap and rotor, adjust your ignition timing +2degrees, MSD ignition coil($30), low resistance plug wires, and a K&N filter. Should be good for a few extra hp, and a few more MPG. If you really want a few more hp, I know a guy who makes performance cam/cam gear combo for like $150. I've heard results of 10-12hp. (20% power increase)

Ok, I know I can find the K&N filter at Canadian Tire (I'm in Quebec by the way), if you can put me in contact with that guy for the cam, I might look for that too, where can I find the other parts?

Oh yeah, also, for the exaust system, for what should I change? I need to change it any way so I'm thinking that I might as well put something better than the stock one.

I also tought about something, my gas tank was changed, but it was replaced by a 30 liters tank. What I would like to know is, if I change my tank, what is the biggest size I could put? I know the stock tank is a 40 liters, but could it be bigger than that or is there a lack of space?