Many newbs have gotten good gains on deca at 200mg weekly - I personally have run a cycle at this dosage and produced good gains.
400mg is not a minimum for this drug (200mg is) and although a good combination with test it is not required for the drug to work. Test is often combined as nandrolone users may find decreased libido (not everyone but a significant portion) - even 100mg of a long acting ester will prevent this and combine well.
Regarding the training and diet, every person on this board says they train and eat well. I have my doubts as I see so few roiders who have any clue in the gym. With deca high protein is essential. Your lifting should focus around squats, benches, deads (or cleans), bent rows, overhead work. If you aren't familiar with all of these exercises (no exceptions) I'd suggest learning them.