I believe when you first plant, it takes 2 days to harvest, but after that is will take 5 days to re-harvest. Different ingredients give different amounts, when you pick them. Some may give 3 of an ingredient when picked, others may give 5, just depends upon the type of ingredient.
The best way to choose what you want to plant is to see what kind of potions you want to make. If you just want for healing potions, I use blue mountain flowers & wheat. If you are going to want to make some blacksmithing potions, then you'll want to plant blisterwort + glowing mushroom. If you plan on making some fortify enchanting potions, then plant snowberries (will also need to collect the blue butterfly wings from butterflies that spawn in the greenhouse). For poisons, then plant : bleeding crown + imp stool -or- death bell. For restore magicka, then plant : creep cluster + red mountain flower. If you plan on making restore stamina, then plant : purple mountain flower + (histacarp , going to have to catch these fish, but if the house with a fish hatchery, that works good.)
As for looks, I think dragon's tongue looks really good, as do the scaly philia and glowing mushrooms. A lot of the 'what looks good' is subjective, and everyone will have their own opinion, plus it also depends if you're looking for flowering plants or just foliage.
Also, if you are on PC, you can get the Heljarchen Farm mod, that gives you a farm, where you have room to plant like 60 things. Is great for alchemy !