Hi
My ds had multiple "minor" issues which added up to lots of stress so we began HE at age 11 too. We are doing our first igcse this summer.
Not much is free but there are plenty of resources and getting exams is common amongst HE.
If you don't intend to go back to school, there is no need to adopt a secondary school curriculum. Just go into the topics which your son enjoys/suggests and bring maths/English into those topics. There doesn't even need to be any written work. It really is up to you. As time goes on you will relax into going with the flow and education begins to happen all by itself in your daytime activities.
For example, 'food' was a huge part of my ds mindset. So we did projects on:
food ingredients (gardening, farm production, factory processes and design, location/geography etc..)
Food transport (history of transport, silk road + Roman Empire, wars/politics in areas of food production, potato famine, green issues, packaging design etc...)
Food as more than food (health, religious ceremonies, family structure/function, chemistry, vegetarianism, food webs, evolution, music&food art&food etc..)
Feed yourself weeks (buy, cook and eat for himself- plus budgeting and finance, recipes, careers in food, law & food etc)
As you can see with one starting topic you can cover any part of the National curriculum (if that is your aim). It just takes a little planning, grabbing opportunities and lots of fun.
As for meeting other children. There will be other HE children around and so they meet up and form groups for trips out, educational visits and sometimes to hold formal classes for exams. Joining a sports club or scouts can help too.
My ds is now relaxed, now has friends and can now write an A4 page easily. This is sooo different to how he was at school.