Audrey,
Welcome to the HQ.
For your first question on o-ring or non o-ring.I personally run non o-ring chains on mine however look for a good tensile strength chain.Ebay ones ussually have very low tensile strenght.Gearing I would run a 13/42 combo and with a +4 swinger you'll have to get a longer chain.116 I believe with that gearing.(2)don't bother with a boost bottle.Waste of money!And as for the leaning out it's ussually not jetting correctly for the conditions or running out of gas.