Looking for advice regarding my hair (colour and possible extensions)

I’m looking for some advice regarding my hair and what direction I should go in next.
I’ve included photos from when my hair was closer to my natural colour and when I used to get occasional highlights/money pieces done professionally. Over time I stopped going to the salon and started using Garnier Olia box dye at home (shade 6.66), so my hair is currently a faded auburn/red shade.

I’m debating whether to:

• keep maintaining the red at home
• switch to a softer auburn/brunette shade,
• eventually try to get back to the brunette/blonde dimensional look I used to have.

My main concern is that I know red box dye is notoriously difficult to remove, and my hair is naturally very fine and already a bit heat damaged, so I don’t want to do anything too harsh or unrealistic.

I’ve also been considering extensions because I’ve always been quite insecure about how fine my hair is. I’d love more thickness/length, but I know I need to decide on a colour direction first before investing in extensions.
For anyone experienced with extensions: are tape-ins suitable for fine hair? or would something like clip-ins/halos be safer?

And for colour: does it seem realistic to eventually get back to a softer brunette/blonde look without destroying my hair? or would I be better refining the auburn/red into something more dimensional and lower maintenance?

I’d really appreciate any honest advice, thank you!