MBH is better if it’s an option for you.
A35 was the best option before MBH was launched, and in some places (notably POSB IS) A35 is the only bond fund offered - which is good, because A35’s still fine.
1- Generally nothing will happen. Your stocks are still safe, because they’re generally held in a ring-fenced subsidiary company that the parent company isn’t allowed to touch. IBKR carries extra insurance as well, to compensate you in case anything does happen. And splitting your accounts across multiple brokers is a massive waste of time and energy. Don’t bother.
2- No, CI coverage is a waste of money, and early-CI is an even bigger waste of money. As long as you’ve got hospitalisation insurance (even MediSave is fine!), you’ve got everything you need.
3- This is a tough question, and reasonable people disagree on it - that’s why I explicitly say in the book that either way is fine. I personally would keep it entirely separate, because if you count your CPF as part of your bond allocation, then your regular account would be basically 100% stocks - and that'd be pretty volatile! It makes rebalancing tougher as well.
I don't know exactly what the fee is, but yes, you're right. A good rule of thumb is to switch over from Stanchart to IBKR when you hit $100k of assets in Stanchart, or when you reach $1k a month of investments.
Not off the top of my head, unfortunately.