You are not going to Olkhon Island? The info I've given for Baikal is to Olkhon Island. For your case, then perhaps 2 days is good for Irkutsk and Baikal.
Most people take the mini bus from Irkutsk to Olkhon and accommodation is usually arranged/included.
Check baikaler.com
Yes I am also heading to Olkhon Island.
Sadly, I found out that the lake will not be frozen in December
The package seems really good. I need to check if they could take a solo traveller as min head count is 2 from their website.

