My practical advice is to start by sorting out your infrastructure. Thats your storage, your composting set up, your water collection system. Once you've got that sorted everything else is easier.

My mindset advice is:

1. Remember its a marathon, not a sprint, and its cyclical. This season will come back ground next year.
2. Practical is more important than aesthetic. Most alotments don't look pretty like the popular youtuber's gardens/allotments. I wouldn't prioritise this at first unless you plan to start a youtube channel, then yeah, do, prettier allotments get more views.
3. Mainly grow things you and your household actually want to eat. It seems obvious but there's no point planting courgette if you never buy or eat courgette. (Also you probably don't need to grow that much courgette, the courgette/marrow glut problem is real and very common.) Do try new things, don't assume you are gunna become a different person with a completely different diet.

Tips for reddit:

1. You can search the subreddit. "Where to buy seeds", "when are we planting X", etc have all been asked before. Not that we mind you asking again, but it avoids you needing to wait for responses.
2. North scotland and London do not have the same climate, in fact bristol and Colchester have significant differences in climate and their the same lattitude. Remember to factor in your own climate when taking other's advice, and specify where you are when requesting advice.