Not that I’m aware — I send probably 5-10 payments a month through Wise (not from India to the US, though), and the fees just scale up and down with the amount of money I’m sending.

They’re regulated by the FCA in the UK, and the equivalent regulatory bodies in many other countries. That means that (in the UK) you’re protected up to £85,000 per account, as with other banks etc that are also regulated. I can’t speak for what the protections are elsewhere – you’d need to look that up based on where you live – but if it’s regulated in the same way as other financial institutions in your country, you should have the same amount of protection.

Who actually regulates them?

You’ll need to contact Wise about this — there’s really nothing that anybody else can do to help. There’s a contact button at the bottom of this page, although you’ll need to be logged into your account to use it.

Not unless the merchant lets you pay by direct deposit into their bank account (which is very rare, but not completely unheard of.)

I cannot get a debit card in my country as yet but am using Wise to transfer across borders already.

That’s correct – if you get paid into a euro TFW account, you then need to pay some or all of the amount out into your usual GBP account and pay the standard fee when you do. The alternative is to get a TFW debit card and spend the euros directly, but that’s only helpful if you have expenses in euros.