publisher is in Japan and the printer is in Singapore.
This is key. The printer is probably very qualified by the publisher. Lots of high quality fine art publication printing use this route from Japan to Singapore.
I would like to improve my color workflow.
You might familiarize yourself with the concepts of G7 methods for the printing process. (Largely based upon measuring and controlling neutral gray balance which, because you’re a photographer, should come very easy to you.)
In the past I would get my images to where I would like them on a calibrated Eizo monitor and then send them off as flattened adobe RGB Tiffs. Results are mixed and I would like to do everything I can on my end to get them files that match what's on my screen.
Just realize and remember your monitor is an emissive device using a wider color gamut than the reflective capability of the given paper. You will need to shift your expectations. Fortunately Adobe 98 is centered upon a neutral axis and some CMYK press standards are meant to be calibrated to aim points of neutral grays. Therefore, both you and the printer might have a common ground at least as far as neutrals, meaning no hue shifts. That leaves shadow and highlight detail along with color gamut. Try to be sure your images have data in those areas because your files will be radically transmogrified, hopefully skillfully, in the production process.
all I need is to proof
You are not actually “proofing” until your print becomes a “qualified” proof. You are merely printing a preview or a “go-by.”
Quoted from IDEAlliance (the G7 folks); “Individual proof verification requires printing the 2007 IDEAlliance ISO 12647-7 Control Strip on EVERY proof, measuring the strip with an automated spectrophotometer, and comparing the measurements to a "reference" set of CIELab values in suitable software.” Also available is a control strip to verify RGB proof prints and many Epson proofs are commonly evaluated only visually. Experienced operators know a practical proof print or go-by from something inferior or unattainable.
I hope this helps.