I did not use that much T3 to prep for a contest.
As for whether 400mg is enough to maintain your muscle, it entirely dependent upon how much muscle you have to protect? If you are a newb, that is probably too much just to "maintain" muscle. If you are a competitor, doing well even at an amateur level, then that is not even close to enough, but if you were a competitor you would already know that.
In short, those who are advising you it is "enough" have no fucking clue and are guessing, because they have never seen you and have no idea what is enough.
Your cut is mainly going to be diet, then cardio, and things like t3 are way down the list of effectiveness. Testosterone is important, but, like I said, how much depends. Obviously the less you can get away with the better.
Do not start t3 week one. There is no reason to do so. Week one should be figuring out your diet - what amount of carbs and fats are necessary to get the scale moving. The first couple weeks cut on diet alone. If you are already doing cardio, then just keep doing what you were doing before (even if it is no cardio) and see how your weight loss goes each of the first two weeks. You should lose weight each week. Then add in cardio over the next couple weeks. There is no reason to start the t3 until you get much further down the road. Pulling carbs or cycling carbs and additional cardio will get you most of the way there.
No reason to ever go over 50 at all, or maybe 75 at the tail end of contest prep if you were a little behind at the scheduled time, and then only for a very short time period. The schedule you provide looks like it will simply eat through muscle along with fat.
Give yourself time to figure out the diet and cardio without "scheduling" weeks of this or that for cardio like you have done. Adjust the cardio based on what you see in the mirror and on the scale, not just because it is week for on your schedule. The amount will be different for everyone. My wife and I prepped at the same time this year. She had to add cardio at the end (am and pm, it sucked for her). I actually had to cut back, as I was way ahead of schedule and my body was burning through calories like a furnace at the end.