is that the dual MPPT or single MPPT model?
If it's dual MPPT, we'd generally combine the strings for each side in parallel on the roof, use 4 or 6mm2 double insulated single core cables throughout (so it can handle any potential fault current even from all 3 strings with ease) then run them down in a single cable so you usually end up with 2-3 strings per MPPT combined, which we've not usually needed to fuse.
If it's single MPPT, then that's a different matter, and you'll probably need to fuse the strings either on the roof, or by the inverter using a separate string fuse unit.
Aurora Power-One do 20 & 30 KW inverters with built in string fuses as an alternative, which is generally what we use for anything that's going to end up needing fusing, and is why I'm a little hazy on how I'd do it with the single string 17000TL.
as to what's the point of the 5 inputs...... I too have wondered that, but I guess it gives flexibility for individual strings with individual string fuses, which might be needed in some countries. SMA build their kit to be versatile for use anywhere in the world to comply with all standards.