For my first village, I am researching level one of all possible items. This takes 8 out of the possible 15 slots.
For defence, my spears have been upgraded to 2, and to help with attack, axes and LC are at 2 too.
For scouts, level 2 is essential, to let you know what resources are left after you have farmed - although level three would be good when we go to war. This has left me with only three slots. I think the remaining ones will go on defence for my main village, although am saving them to see how things progress. They are quite expensive, and not essential to me yet.
For my 2nd village, all upgrades will go on defensive units (no rams, cats etc. and scouting missions will go from my main village).
Then when I make a further attacking village, all upgrades will go on attack.
These are just my views, and would welcome any further input if I am making a huge mistake.