Using a cheap vert water smoker...

My first attempt at smoking went well - whole chicken @ 250 for 4 hours. I
didn't add enough charcoal to start so I had to add some twice during the
cook.

Now I'm 2 hrs into cooking:
This time - ribs - I added plenty of coal to start, but I can't get the temp
below 275. To maintain 250 I have to leave the lid a little offset. Also,
I tried the wood chips in double wrapped foil, but the foil burned through
in the first half hour - no more chips. I'll have to periodically add a
handful of soaked chips throughout the BBQ session (that's what I did with
the chicken).

How can I get/ keep my temp down?

How much of an impact will 250 be on the ribs vs the 225 I want?

Thanks for your help!