Andrey Azimov

How to incorporate a company in Singapore?

You can have a look at, but seems like a very interesting option.

Pete Codes

How do you sell SAAS products overseas and handle tax?

Yes, in your case you will most likely only have to pay taxes in the UK on Australian and American profits, unless you have physical operations in those countries that generate profit. On EU profits on the other hand, you have to deal with the maze of VAT for each customer. If you were to sell physical products, then it's different story.

Ernst Mulders

Should I inform the user that its a paid service before or after he submits his email address.

If you don't let a potential new user know upfront, it can feel like a bait and switch, something that is annoying and can hurt your reputation.