Thankyou for agreeing to 'reconstruct' my bag. I have noted some of my own ideas below just to give you some idea of my 'bag personality', though I have complete confidence in your ideas and designs from what I have seen on TV!
EXTERIOR (Overall bag height 30 to 35cm will be ok)
Smart-ish (I quite like vintage styles)
Stylish
Straps on back of bag to sit neatly/closely on your back (so that bag doesn’t fall backwards when placed on your back) to be worn as a smart-ish rucksack style and shoulder bag (using the back straps to place on shoulder??) with a small handle on the top of the bag so that it can be carried like a ‘traditional handbag’ when not using as a rucksack or shoulder bag.
Simple, stylish exterior and interior (perhaps making use of existing interior material).
One pocket on outside of bag (front of bag) for quick access items like car park tickets/bus tickets/small non-important items that need to be got out quickly (perhaps zipped or magnetised closed?? but not overly important to be secured closed).
Use what you can of the ‘old’ bag like the clip mechanism, if viable. I quite like a clip opening rather than a zip, as zips take time to open and can often get stuck or not run smoothly and can break (so zip not preferred on the main top opening of the bag).
INTERIOR
Roomy interior, with one inner pocket only, to house mobile phone with casing: 18cm x 10cm (this allows comfortable fit / putting in and getting out).
If there is room for another pocket to house car and house keys, this would be good so as to avoid ‘hunting’ around for these in the main body of the bag, but not essential if the interior room is not available.
I would rather have plenty of interior room for general items such as purse, store card wallet, lipstick holder, glasses/spectacles case, plus room for a collapsible umbrella if possible!
Please be aware that although the leather is beautiful, it is reclaimed and saved from landfill so does have imperfections, these wont detract from the end result, in fact, they show their backstory and that you care.