Clipless pedals make you 30% more efficient because you get to pull up as well as push down on the pedals.   This comes in handy on long days when your legs are tired because you are using different muscles.

Don’t worry about falling down because everyone does it starting out.  I still fall once about every year at the beginning of the season.  It generally doesn’t hurt if you do it right (tuck and roll on your back).  Putting your arm out to break your fall can break your collar bone.

I prefer sandals, but get something with a recessed cleat that makes it easy to walk around.  Cycling shoes will acctually help your foot problems.  Having a hard sole spreads the pressure of peddling over a large portion of the foot.  A good fitting shoe will ease pressure on and off the bike.