Critique my first large batch mash please

[jon1163]

I just did my first large batch fermenting and was hoping that I could get some of you guys and gals to tell me what I did right, wrong, and what could be improved.

Recipe:
18 gallons
18 lbs flaked maize
6 lbs 2-row
3 lbs Brewer's malt
3 lbs rolled oats

Notes:
I mash in a 30 gallon barrel and have no way of heating the mash after it's in the barrel.

1. I boiled 18 gallons of water and put it in the barrel. I added my corn and oats and used a low speed drill and mortar mixer to stir the hell out of the mix. When I added the grain the temperature drop to 185 degrees.

I steep the corn and oats for one and a half hours stirring with the mortar mixer every 15 minutes.

When the temperature dropped to 155 degrees I added my wheat malt and stirred again. The temperature then dropped to 150 degrees.

I added 3.5 teaspoons of amylase enzyme and start again. I waited one and a half hours stirring every 15 minutes.

I called the mashed about 78 degrees and took a starting gravity reading of 1.055. I had three packets of Safale US05 and aerated well.

After 8 days my grain cap fell and my final gravity was 1.005 for a 6.55% mash.

Any advice on how to better my process?

Thanks in advance.