/fa/ - Fashion

I should probably clarify some of this, before I drift off into the abyss of sleep.

1) Thin hides like Lamb are used primarily for fashion leather and fine leather goods; it's inappropriate on a double rider, because you're looking for something that is protective (function, then aesthetic). Steer and Horsehide are the more common and traditional leathers for this, that's why I say go with it and NOT a fashion leather. There's nothing wrong with lamb, incidentally, but it's more suitable for leather coats that go over suits, purses, and other luxury items. This style of jacket is not a luxury, it's a practical coat of armor (before the invention of synthetics).

2) Custom sizing is ideal, actually, unless you're blessed with normal proportions (given that you're 6.4, I doubt this very much). It's a little more expensive, but usually not too expensive. But it's worth it, because if you're going to spend above 700 for a leather jacket, you might as well get it made to your specs. It's a waste of money otherwise, because an ill-fitting jacket is one that will spend more time in the closet than out on the town. Also, given the hardware on jackets (zippers, buttons, etc.) it's usually easier to get it custom made by a company than to have it altered after you get it, so bear that in mind.
3) Wearing in a new jacket is a process that is fun but a little annoying if you're not used to it. The quickest way is to get it wet, and then wear it fully zipped up (not wet on the inside, just on the outside). Some even go so far as to wear it in the shower for a moment. The point is that the leather will bend and crease according to your personal body shape (elbows, shoulders, etc.) and after it dries it'll 'set' to some degree. Now, this is not reparable in any sense of the word, so only do this if you're sure you're keeping the jacket. If you try to resell it after it has significant creases, the value drops for obvious reasons.
Hope that helps.