Why I'm not looking at installing OmniOS via Kayak
As far as I can see, OmniOS's Kayak network install system is the recommended way to both install a bunch of OmniOS machines and to customize the resulting installs (for example to change the default sizes of various things). However, even setting aside my usual issues with automatic installers (which can probably be worked around) I've found myself uninterested in trying to use Kayak. The core problem for me is that Kayak only seems to really be supported on an OmniOS host.
The blunt truth is that we're not going to use OmniOS for very much here. It's going to run our fileservers, but while those are very important machines there are only a handful of them. I don't want to have to set up and manage an additional OmniOS machine (and a bunch of one-off infrastructure on that machine) simply to install a handful of fileservers with custom parameters and some additional conveniences. The cognitive overhead is simply not worth it. Things would be different if I could confidently host a Kayak system on an Ubuntu machine, as we have plenty of Ubuntu machines and lots of systems in place for running them.
I'm aware that there's some documentation for hosting Kayak on a Linux system. Unfortunately 'here's what someone tried once and got working' is not anywhere near as strong as 'we officially try to make this work and here is information on the general things Kayak needs and how it all works'. One of them means that people will take bug reports and the other one implies that if things break I'm basically on my own. I'm not putting crucial fileserver infrastructure into a 'you're on your own' setup; it would be irresponsible.
(Well, it would be irresponsible to do it when we don't have a relatively strong need to do so. We don't here, as manual OmniOS installs are basically as good as a Kayak install and are considerably less complex overall.)