"If you win the toss - bat. If you are in doubt, think about it - then bat. If you have very big doubts, consult a colleague - then bat."
I think you should play to your strengths, you say you don't chase well but can restrict teams. Sounds like you should bat first if given the option. Do you have a new ball per innings? Are your bowlers line and length or rely on pace?
On the other point friendly or not you should aim to bowl teams out, Pointless practising keeping teams in the game. If the game finishes early play a short T20 or something. Youll get more out of that as opposed to engineering a result.