Of course the answer to the first question depends on a number of factors - how cloudy is it and for how long is it cloudy? How depleted are the batteries to start with? I replaced my lead acid batteries (400 ah) with two 230 ah li batteries thus just about doubling the usable capacity of energy. But, my actual usage has stayed just about the same as it was before the upgrade. So, my standard Oliver solar panels have absolutely no problem fully charging these new batteries to 100% every day AND I have plenty of capacity in the event there are several days of no sun.
Asking about brands of batteries is akin to asking about brands of truck, cars, etc.. To each his own. For what its worth, I purchased LiTimes and have had zero problems. However, I understand that Epoch is making a nice battery and, of course, there is always the higher end Battle Borns. Check to make sure that the manufacturer is using #1/grade A cells and then it is a matter of the features that you might want/need (i.e. bluetooth, heated, on/off switches, etc.).
I'd wait on the DC to DC charging until you have the experience with the new batteries. If you actually need the extra charging then you can add it later.
Bill