I worked with a small (4 to start, then up to 20-ish) group of people for about 20 years, starting at a university research group, moving to a startup, through prototype, early product, pivot, and finally to mature products. Always spread over multiple continents: Europe, US, and Australia.
You need some facilitating technology:
* A good chat system. Slack is ok, but its message threads are terrible. And threads are really good for context, which is really important if conversations need to spread out over time.
* A shared whiteboard. Lots of people think well while diagramming, and it's a great way to communicate ideas and evolve them. There's a lot of bad whiteboards out there. It's probably worth buying a big iPad and pen for everyone just for this: if you have to use a mouse and draw like it's Visio, you've killed it before you start.
* Integration between your repository (git?), your CI system, and your chat tool. When people aren't in the same room, or at the same coffee machine, this is a great way to build peripheral awareness of what's being done.
* A wiki, but ... it's useless unless the culture is built to make curating it part of everyone's responsibilities. Given timezones, you need information to be available in written/drawn form. A badly manged Wiki is just a dead zone, but a good one is a fantastic resource for coworkers (and your forgetful self!).
* A final tech thing: we found that keeping a daily, public log of what we'd done and how we'd solved issues was useful. Just a few bullet points, a few cut'n'pasted command lines, and some text explaining what and why. Aside from documenting solutions to problems, it's also a great resource for seeing how things developed to where they are, and why. If you keep it in the wiki, it can be easily searched, and becomes part of the shared knowledge.
So far as timezones go, there's advantages to being far apart: Asia/Australia and east-coast US for instance means you get two chances to catch up in real-time every day, whereas Asia/west coast is usually just one. Realistically, you need to be flexible about work hours: a quick check of messages when you wake up (possibly logging in to resolve urgent stuff), early calls, then a break before work proper, then a break in the late afternoon before a late evening check, answer questions, and maybe another quick call. Everyone kinda needs to be committed to this, while realizing that it can't be _every_ day.
Calls/video/meetings are productivity killers if they happen too often, or run too long. Treat them like they're costing you a lot (and they are).
So far as early-stage customers go, having folks in different timezones can help a small company to be super responsive: someone can work on a customer query or issue overnight, and you can get back to them first-thing the next day. It really helps you look professional.
