Depending on the lay out of the rooms a hallway to get to a new door would eat up a lot of inside space. If there's just a living room behind that area it might work. If you do go with a door order it out opening, left hand, vinyl jambs and brick moulding and adjustable threshold.
Looks like a slab house that was built to close to the ground so the T-111 siding is all rotted at the bottom, no quick, cheap fix.
A rental I own is almost the same size as this house. We cut out the bottom 2' of T-111 replaced it with Advantec Installed an L shaped piece of coil stock along the botton of the sheathing running it up 4" to help keep splashed up water from getting to it. We added tyvek, then a piece of 1 X 6 vinyl lumber along the bottom, a piece of Z moulding, a piece of J moulding then sided the whole house.
We also added a roof over the doorway. It made the house look bigger.
The plan is to also add a walkway which yours would also need so you do not track grass in.
I'll try and post a picture of the before and after tonight.
It came out good enough I could charge more for rent and people I had never met before came by to say how nice it now looks.
Another reality check on old slab houses like that is at some point the supply lines will start leaking if there copper or steel.