If you are applying for a fiancee settlement visa (which I presume you are) ...
Does my fiancee need to give notice to Marriage registrar or Just have to apply for COA
You won't need a COA - your fiancee visa is effectively permission to marry already. You will have to follow appropriate procedure for the registrar though (which I can't testify to as I used the CoE).
Also how much time will it take to get spouse visa after we get married as i need to leave the country for my business commitment ?
You could use a same day appointment for a premium in order to get around that.
As my business commitment needs travels does in future applying for ILR do I have to be in UK far all 24 months straight ?
Business travel is acceptable - but you have to show that you're in a subsisting marriage. Being out of the country the vast majority of the time might well count against you. But - going for citizenship has specific time out of country requirements and you should read up on this.
This actually leads to a wider topic as one of the requirements is that you need to show for the fiancee visa that you intend to live together permanently once married. Now, if you already have business commitments abroad, what is the likelyhood that you won't actually be spending enough time here for it to be regarded as a subsisting marriage?
Please also keep in mind that you can't be employed in the UK on a fiancee visa.
M.
