Are you going for 501st approval? The vest needs to be long enough to tuck under the girth belt.
Line copied from 501 CRL;
Vest is long enough to be worn under the girth belt.
My vest was actually a little too long and was coming out the bottom of my girth belt. So I ended taking some shears and trimming it. It is definitely better to be too long than too short. Since the bottom of the flak vest is not seen when fully suited up, a seam with piping along the bottom edge of the vest is not necessary.
The neck hole on mine is also quite smaller than that of yours. I actually have to turn my head to the side to slip through the hole, even with the shoulder Velcro undone. Once I am through, it closes up snug around my neck.
The belts can only go up so high on the body. The girth belt overlaps the top of the cod piece a little (see photo below), and the cod piece can only go so high before it becomes ahem....uncomfortable. Especially for us lads.
Another line from 501st CRL;
Codpiece is worn under all of the belts.
As far as armor placement, when you are ready I would definitely start at the top and work downwards, instead of at the bottom and work upwards. Meaning, mount your collar armor first and then base the position of the other plates off of that. Who is going to see where your belly button is under your suit in relation to your armor plates when you are dressed? What matters more is that the spacing between the plates is correct.
Another Jango costumer sent me this photo when I asked about chest armor placement and it was a TREMENDOUS help to me when i started mounting my armor.
The points and edges of the armor line up with each other.
I suspect the advice you are getting from your local clan is geared more towards what they are familiar with, that being the requirements that go along with building custom Mandos, and not that of replicating a specific canon character.
How tall are you? Temeura Morrison is 5ft 7in. If you are in that range it should look pretty close to proportionate to the real thing.
An unrelated side note, your flight suit looks to be a little too deep or dark of a blue. The 2 variations the CRL lists that are accepted are a slate blue or that of a blue-purple (aka Blurple).