Hi Ash,
Good luck! If I calculate correctly, your bed will be about 8' square - that's not much so you'll need to be careful how you lay stuff out. You might find 'square foot gardening' a useful search term for info on gardening in small spaces.
The type of tomato will dictate whether they are self-supporting or not, but if I were you, yes I would put canes up against the wall to support tomatoes.
Re the chillies and peppers, I believe they usually do much better under some form of cover e.g. a mini greenhouse - but others may well know better as I'm not really a chilli / pepper grower.
You might want to consider using a salad or first / second early spud variety rather than a main crop, as they have closer spacings and so you're more likely to get a few more tubers in.
I'd suggest that you check which way your sun shines, as if the wall is north-facing then I doubt anything in the bed will get much sun. It is also true that north-south rows allow slightly more sun to get to the plants than east-west rows, so if this is possible it might be worth considering.
Also, walls tend to create rain-shadows so you will need to make sure you water plants next to one much more thoroughly in dry-ish periods.
As for preparing the soil, none of your plants are parsnips or carrots, so I'd simply suggest putting manure or fertiliser down at some point in order to improve what will probably not be very good quality soil.
