There are a lot of "Chinese" restaurants in this country, mostly offering the same, not very good, fried food. Don't be like them.
Outside of London, places serving good Cantonese food are very rare though. I reckon if you did that, you'd be very successful.
This is a great way to go bust quickly. This is literally the worst, possible advice.
I grew up in Chinese restaurants and been there, done that. My little Chinese mother packed me off to a Chinese restaurant when I was a teenager and while it wasn't my thing, I saw what worked.
To answer your questions:
1. Hiring a chef on a working visa... well, forget about it. The Chinese restaurant owners I know used 'backdoor' solutions of varying degrees of legality, lodging chefs in private accommodation while they were here.
2. Renovation estimates for 3,000 sq feet: £200 per square foot is the general rule for a complete transformation although this varies according to what needs to be done. I know the guys who renovate specifically Chinese restaurants and can put you in touch with one if you want. They would need to know what needs to be done.
3. If you have a ton of experience around businesses, you will understand the restaurant business.
Chinese restaurants are about location, marketing, positioning, pricing and experience plus distribution if you're thinking about the delivery business, just like any business. Recruitment is a challenge with several solutions. There was a dumpling chain which did well which preceded Wagamama and my family helped the owner with the menu, accounting, staff and a few elements around the experience. I worked for the owner as well but again, a lifetime away, and this was absolutely no different from any other business. Positioning, brand, marketing, pricing, location etc... were all critical and you can figure this out although having an expert advising you can't hurt.
Happy to connect you with a multi-millionaire former restaurant owner who'd probably be happy to help. He's an ex-Hong Konger from back in the day and can talk you through what works as he's now retired and probably a bit bored.
I'm in video production now and not interested in the Chinese restaurant business but happy to have a chat if you DM me.
Like any business, it's about creating the right package.