Dear CarrieP,
I successfully used the cold cap this year, and I would definitely recommend trying it.
I also had my eyebrows microbladed after my Mastectomy and prior to Chemo.
I would assume it would be wise to have eyebrow tattoos done prior to starting Chemo, if you want it done.
Once that you have started Chemo, you will be more prone to infection, especially if your White Cell numbers drop as they often do on Chemo. Depending on the time frame that you have, you may not get your touch up prior to Chemo. If you don't ask if they will do it after chemo, they may be sympathetic.
I finished Chemo in August, and still have few eyebrow hairs. But they weren't thick before.
I missed my eyelashes too, they grew back 2 months after chemo.
Good luck with your decisions, and your future treatments.