With supply lines; should they be inter-connected or not? At the moment my centre settlement (and my original) is Sanctuary, all other settlements lead there as it were. Should I create more links?
Interconnection isn't necessary - links can't be broken (provisioners can be attacked, but not killed), all settlements on a supply chain are treated as being linked and there isn't any time delay. The length of a link also seems to be irrelevant.
When you get more settlements you won't be able to link them all from a single settlement because you won't have enough settlers at that settlement to provision every other settlement.
If you like having one settlement providing the provisioners for many other settlements you could do that with 2 or 3 settlements with a link between the groups.
e.g. A provisions B,C,D,E,F,G,H,I,J and K. L provisions M,N,O,P,Q,R,S,T,U and V. Link any settlement in the first group to any settlement in the second group and all settlements in both groups are linked.
Also, how do you keep all your settlements happy, what's the trick? There must be one
Happiness ratings up to 80 are quite straightforward:
Enough food
Enough water
Enough beds in shelter
Some shops (with shopkeepers, i.e. working as shops)
Enough defences (not a direct effect, but attacks reduce happiness if they're not killed off without loss to the settlement).
A dog increases happiness too, by 5 as far as I can tell (my Sanctuary, where Dogmeat lives, tops out at 85 whereas other equally or better equipped settlements top out at 80).
To get above 80 (or 85 with a dog), you have to get a bit silly with optimising settlements for happiness by making a
lot of shops. You can get 100 by having 18 settlers with 15 running shops and 3 farming to provide 18 food.
Decorations, defensive walls (my major settlements are full on castles with thick stone walls 20 feet high) and entertainment options (radios, pool tables, jukeboxes, chessboards, gyms, bowling alleys, basketball courts, etc) seem to have no effect at all.
TVs are linked to a serious bug with settlements and are generally not recommended as a result. They probably have no effect on happiness anyway, since other entertainment items don't.