I would like to know if you can own all the houses and have stuff in all of them or would that be a bad idea?

These are all the houses you can have right?

1. Breezehome, Whiterun (Whiterun Hold)

2. Hjerim, Windhelm (Eastmarch)

3. Proudspire Manor, Solitude (Haafingar Hold)

4. Vindrel Hall, Markarth (The Reach)

5. Honeyside, Riften (The Rift)

6. Severin Manor, Raven Rock (Solstheim)

7. Lakeview Manor, (Falkreath Hold)

8. Heljarchen Hall, (The Pale)

9. Windstad Manor, (Hjaalmarch Hold)

Any help would be great

Yes, you can.

You can own every house. I've done so on multiple characters.

Be advised though that Hjerim requires you to be a Stormcloak and to complete the Ford Neugard quest - or to be an Imperial legionnaire and win the Civil War.

If you're on the PC, there are mods that bypass all that...

I've only ever purchased Breezehome from the Vanilla list. I enjoy a few house mods though.