As far as aluminium tube sizes go, I bought the same motor as @Talkiet linked (due to an earlier post of his :), but wanted to motorise just one of my existing cheapie Spotlight blinds (a very long one covering the window to my stair landing).

The existing tube had a very narrow diameter, so once I got the motor I just took it in to a local blind place I was passing (Just Blinds in Wellington) and they sold me a tube with the correct internal diameter, cut to the right length and with the fixings required to mount it. I then simply detached the blind from my existing tube and attached it to the new one instead.

Sounds like I have a similar setup to Talkiet - using HomeAssistant and an RMPro I have it automated to shut ten minutes before sundown and open at 8.20am on weekdays, or can use voice commands ("Hey Google, Shields Down")

I hadn't seen the Xiaomi ones before - as I use their home hub and a lot of their switches and sensors etc, I might have chosen that one instead as I've found their gear to be very well built for the price. I did have huge issues with getting my blind motor in, as because it has an internal battery it was held by customs in China for three months before being returned to the seller, and I then had to pay an extra $50 for shipping to use an alternate carrier.

As far as track curtains go, it looks like my Slide controllers are just about ready to be sent, which can be used with existing curtain tracks and will integrate with Home Assistant. I pre-ordered them on Indiegogo a long time ago, but I'm relatively fine with the delays as they've given regular updates and have spent the time improving the quality, reliability and manufacturing process before shipping, which is now due to happen in September. 

EDIT: I've just looked at the current pricing mentioned on the Indiegogo page, and definitely wouldn't have pre-bought at that price. I think I paid around NZD$250 including shipping for Slides for two sets of windows. I can post an update when they arrive.