Hi op.
Youre not automatically ruled out of shared ownership if you already own somewhere else, but you may have to sell it first. So sell the place you're in, live elsewhere then apply for shared ownership. Shared ownership is there for people who can't buy the equivalent outright. But if you can buy outright do that.
In some areas shared ownership is very desirable. Where I am (London) I applied and was unsuccessful several times before getting my place. I got this place because I lived AND worked in the borough and had a 15% deposit for my share.
Staircasing is a good idea if you can do it but it can be expensive. You have to pay valuation and legal fees each time you do it. It cost me nearly £30,000 all in to put down the deposit and pay fees on a 40per cent share of my flat. So it really depends on your circumstances and money
BUT I have a lovely large flat in a good location I like rather than wholly owning a crappy small place really far away from my job/interests/friends etc.
Shared ownership places are owned and managed by housing associations even if it's in a private development. The shared ownership places are sold/handed over to housing associations as part of planning conditions.
I recommend buying a shared ownership flat built by a housing association on one of their developments - they have a long term interest in managing those estates well. Private developers often chuck it up and fuck off. They don't care. Housing associations have a social purpose and care about the place and it's people not just profit.
Yes service charges can be expensive and most places are leasehold. It is what it is.
Rent rises are capped.
You cant be evicted.
You can't usually sublet the whole home, but you can usually take a lodger.
Shared ownership is better than no ownership.
Will do my best to answer any other questions.