I’m not a professional, and i can’t answer all of your questions, but I have some experience and can give you some tips.
No idea, I don’t use many plugins
There is no one best style to use. You can use whatever style you like. You should however try to keep it consistent and readable.
No.
Practice makes perfect, don’t be afraid to try out different styles and ideas. Use inspiration and tutorials if you need help, but don’t be afraid to do your own thing.
What are some of the best plugins to use? : “UIBlox Icons Plugin” you can have roblox icons with it and “autoscale lite” scales for all devices and “UI Shadows” (100 robux adds shadow)
What is the best style to use? depends on the game your working on i mostly use cartoony style
Do you have any screenshots of your previous work? : yes.
How can I improve overall? : mostly just messing around learning about the features in roblox studio or photoshop to make ui or just learn from videos! if you really want to do a style i suggest watching someone make it in yt tht could help since you can understand it.
make something , share it with people and ask for criticism
according to my experience in the talent hub the most requested style is the cartoonish one , but that shouldn’t stop you from learning other UI styles
Roundify it just helps to make your text more modern or better looking
use whatever style you like most. Just go in studio and experment with diffrent styles and find some you like.
3.no
If you do want to improve look at other peoples UI deisgns and take insperation from it. UI will not look the best at first but later on it will start looking better.