Congratulations on your purchase.
For tyres, as advised earlier, go for 18/65/r15. I am using them on my city which I bought last March. Thats the ideal size for both comfort and consumption. I opted for Yokohama C drives but I believe they aren't in production anymore. Yokohama BlueEarths are the new ones I believe.
Speakers you can install any 6.5 inch ones in the back doors, but as said earlier don't expect miracles with the stock head-unit. I had a pair lying around so I have put them in.