There’s already been requests for some of the features you listed
Please support the existing requests
Roblox has several shapes in their texture folders that we can use in games, one of those is a rounded rectangle rbxasset://textures/ui/RoundedRect8px.png
However I find it very much a hassle to constantly go through the textures folder just to find something that can be used, so I support this request.
Roblox also released a survey regarding UI tools recently, but these most likely will take a while to get added.