Ok, my last question was answered,thanks again by the way.......but I have..

Lets see if we can do this systematically.....

You will buy things at the store every day that it's open. I know they close during the week (Tuesdays I think). Once you do that, a sprite will be released that enables you to buy stuff over the TV shopping network. This is where you'll get the oven, big bed... Etc.
Keep checking Gotz the woodcutter. He will let you pick "house upgrade" on his list. You can do this twice, and it's pretty expensive, but necessary.

SPRITES:
You can definately check on your sprites in the menu screen.
Click on the menu button (the 4th one down on the left) and then scroll down to the little red picture of the sprite. There should be a number after it. This is how many you have rescued. Click on the sprite, and it will list them all by name and show you how much they all like you! Give them flour while they are working, and they will be so excited!!!

Well... I won't answer your questions in the order that you asked. Instead I'll answer in what I did first.
Yes, the supermarket isn't always open. It's their day off every Tuesdays and Sundays. Personally, I don't think it has to be in a row. I didn't buy for 10 days straight! In one of my files I unlocked the Shop on a summer. That was when I bought something(after not buying for several days) and the next day I unlocked Venus.
After unlocking the TV shopping network, you have to buy the table before the 1st house upgrade will be available. You have to call him via telephone and hire him for the work. You also need 200(I think) material stones for the job. Or you can just purchase the whole thing from him.
As for the sprites, you open the... Ummm... The little icon on the touch screen that looks like a small you. There's another icon there that looks like a sprite. If you touch it it'll show you all the sprites you've unlocked, including their names and colors.