which to purchase first - aerobars or pedals and cleats (Page 2)

clipless pedals and cleats. 

Set the bike on the trainer and do 1 min sets of 1 legged peddling for the first 10 min of your training ride each day. 
For the rest of the training ride, focus on moving the top foot forward and the bottom foot backwards.
After a week, take the bike outside and head toward the nearest hill.  You will realize what you just gained as you no longer smash down left - right - left - right.  Instead you will be smoother and use a lot less energy since you will be using both legs to generate power.

At least that's how it worked for me.  I really noticed how much mine helped after using them on the trainer. 

I actually went with the aerobars first...was riding with toe clips rather than clipless pedals for quite awhile (including through first two tri's).  Might have gone the other way if I had it to do over again, but maybe not.

I would go for clipless and shoes as well.  Most look at it as an efficiency gain, and while that is true, I think the greater immediate benefit will be in cycling form and bike handling skills. 

for sure clipless! 

pedals/cleats for sure!