but i don't know what you are using to charge with? genset? windgen? hydro?

i imagine each would have its own seperate concerns and how best to do it.

perhaps you could charge the whole lot together and only divide the strings for equalization periodically, that might be more practical.

there was a guy on ebay that sold some monster dc contactor/relays with 48volt coils
and 300amp capacity a while back, all new take outs made by prestolite.
the priceing was very good in my opinion, i got 4 of them in 24volt coil configurations for my system.

your probably going to need to divide the strings for charging  and certainly for equalization in my opinion.

They are 20 years old I obtained them at age 13.

I would concider two strings normal, in my opinion the main difficulty of so many batteries is the time required for maintaining them.

So if you need 3 strings go for it.

Beware of perfection. People get hung up on often ridiculous ideals.

If the impedance of each string is equal then the number of strings does not matter.
Key words "impedance of each string is equal".

Again beware of perfection. I used bus bar to connect my batteries together, much lower impedance than the battery. Not a worry.
Some might suggest to connect the middle of the strings together, not sure I would do it. I would start out without, measure it over a period of time, if they were different then might tie them together.