Yes you need to go into the loft and crawl into the eaves and feed your wires through

Yes IP 65 230 volt down lights you require, they have their own integral driver. However, they are not ‘waterproof’ they are Weatherproof-big difference. But they are only weatherproof if installed correctly.

You can use ip65 or ip68 rated (means water proof) led light strip which has adhesive tape that allows you to fit by peeling off on a continuous reel to conceal on the underside of your soffit.
You will need the correct driver for the rated LED which should be kept in a dry waterproof ip rated box you can use a variety of led,s i.e. warm or cool or multi coloured led this could be and option instead of trying to replace existing soffits and facia boards.
I hope this has helped you in looking at alternative way of providing lighting

I myself would not recommend fitting any electrical appliance out side without a qualified electrician water and electric don't mix if you have a box sophit under the wall plate then it will be very difficult to access and would require the sophit to be removed.