Sanctuary, size is in yellow and i am randomly losing happiness, everything else is green, i have like 80 defence, 18 power, 10 people, 18 beds, 18 water and like 24 food.

I have Two radio towers set up on the opposite sides of my town.

What does Size yellow mean and why am i losing happiness, and why does the map indicator say i only have 7 people when I have 10 from the workshop screen?

As for your size, yellow just means you're close to your build limit. When that bar gets full you won't be able to build or place anymore items. As far as unhappiness, sometimes it gets stuck for me and if I exit and fast travel or something, it tends to change to the appropriate level. No idea about finding people. I lose them all the time.

Your settlers are not happy when it rains and they are working the plants though I don't know how to avoid this, it isn't like we have a meteorologist around to get weather updates. I saw someone mention greenhouses can help with this but I can't build such a thing so not sure if that is even in game.

Build some decorations - pictures, rugs, furniture. Get some electricity wired up to the living quarters to get 'em some light, pop down a spare radio.

If all that is sorted, build Traders - rich settlers are happy settlers.