Is 400 mg of diphenhydramine to help sleep to much?

Definitely. 400 mg is the maximum daily dose for severe allergic reactions, in a hospital setting. For sleep, 50 mg should be the maximum, to avoid both unpleasant and even potentially life-threatening adverse events. Central nervous system effects are particularly significant. Even for "benign" meds, packaging dose limits are not suggestions; they balance efficacy with safety and should be followed.
Benadryl (diphenhydramine) Thats a lot of Diphenhydramine can cause confusion, delirium, heart attack, impaired judgement performance for 72 hours or more or even death.