I think it's better to start out with an itemized list of what you want to power instead of just jumping in with system design. Could you list what it is you want to power? Is this for a cabin, or maybe an RV?
I see you mentioning DC lighting, and pumps, but can you go into more detail as to the number of watts you need? What kind of pump? Just a transfer pump, or a deep-well submersible pump. Details up front will help us help you design a better system that is not going to let you down. What you need to power, along with what you can afford to buy tempers all the decisions.
As MY general rule of thumb, I'll give you system sizes as I like to plan them. Of course others here will find exceptions to my rules.
12V: loads less than 1000W
24V: loads 1000-2000W
48V: loads >2000W
I've managed all three, though now for myself, I've settled on 24V and 48V systems to meet all my needs. I personally have given up on DC completely, running both my cabin, and workshop on 48V and 24V inverters respectively.
Let's say you do decide to make yourself a 24V system. Yes, there are DC to DC converters you can buy to supply power to those 12V items you can't part with. Pay close attention to the amps that what you want to power consumes. Most items though probably will be supplied OK with a unit like this, that handles 20A. This is just one example. There are other higher amp capacity units. Price goes up as the capacity goes up.
