Re: Dragon Age origins Ultimate edition does not support modding easily.
There is a 4gb patch you may need to install (look up NT Core 4gb patch). I also have DA: O Ultimate Edition and am running about 14 mods with no issue. I am also using Windows 10, but launching the game through EA Origin.
You don't need a mod manager for DAO. You may need 7zip to unpack some mods, but almost every mod is copy and paste into Documents/Dragon Age/packages/core/override. If you do have a mod that's in 7z (7zip) format, you'll have to use DA Updater (in the bin_ship folder of your game folder, wherever that's been installed) to install those mods.
What I can suggest with your mods is make sure they're coming from Nexus. Every mod hosted there is tested for viruses and problems. If you absolutely HAVE to have a graphics update, I can suggest RDP (Realistic DAO Project), though it's incredibly memory intensive. You'll be rebooting your game every 30 minutes or so. DAO is 10 years old, it's going to look 10 years old.