I'm in the same boat as you, more or less, but am considering getting some cheaper customs for my first pair, to see if it is a thing I like and will work for me.
Which has me inclined towards getting the Heir 4.A. In part because it's $450 rather than $1k, and in part because I can sell them to anybody and that owner can get them reshelled to fit them personally for only $70. So even if I hate customs, I'm out relatively little money for trying them. Other manufacturers have other ways to keep customers happy: Unique Melody doesn't have the same second-owner policy as Heir, but they will perform upgrades for relatively cheap, so you can start with a smaller investment and then go all-out if you like where things are going.
On the other hand, I already have a portable amp that I think is fantastic (Leckerton UHA-6S) so all I really need are the earphones now. But not to muddy the waters, if you have only $1k to spend, you might be better off getting some custom IEMs that cost less than a grand and put the rest in a good portable amp and a line-out dock.