As others have said a tray isn't a good idea. Galvanised feeders are fine but there are also several good plastic gravity feeders available which are easy to use and keep clean such as
http://www.molevalleyfarmers.com/mvf/store/products/6kg-plastic-super-feeder;jsessionid=D471B13CEBB215C13BDF8A5EF5BDE38E#descriptionThis is a 6KG feeder, a hybrid layer will eat 850 ish grams a week so this will give you some idea how long a feeder full will last. There are smaller 2.5Kg ones available if that's too big. It's a good idea to allow above 4 days worth so you can go away for a long weekend without needing the sitter / egg collector to refill. Any longer than 4 days worth and it may become damp. You don't need a lid just suspend it at back height (above their vents). They need to be kept in the run undercover not in the house.
There's similar a 4litre drinker also available I like to have two in case one gets knocked over. Chx drink around 200ml of water a day depending on the temperature of course. (A little more in summer and less in winter).
Avoid the cheap red plastic ones as thes have no UV filler in the plastic and quickly go brittle and crack. There are good quality thicker plastic red ones about too and I believe Joyful uses a good quality plastic one which costs a little more. I'm sure she'll tell you about where to buy them.
A gritbox is usefull too for oystershell and insoluable grit.
It's always best to get purpose designed feeders & drinkers etc as it's hard to beat the experience of design which these have. Dishes and pans etc always have drawbacks.
I'll leave the DE slurry to another post.
Happy keeping
HF
PS Lindeggs if you are going to feed whole grains you will need to supplement calcium preferably in the form of 75 % limestone flour and 25% crushed oystershell. If you add to their feed work on a Ca requirement of 3.85gm/hen/day for laying hens during the first laying cycle.
Poultry Spice might be good too from time to time. I say this as an all corn/ grain diet for layers maybe lacking in essential minerals.