If you are buying Shared Ownership, some of the general advice may not apply in exactly the same way.
You have to be accepted onto the Shared Ownership scheme first.
This means your income and savings must be low enough that you can't afford to buy on the open market, but high enough to be able to afford the mortgage. You might have to meet other criteria like having a local connection or being in a "key worker" job.
Your purchase is likely to be the leasehold, which means that the Shared Ownership company has the freehold. They will own the building, you will own the right to live there.
You may well pay for buildings insurance within your annual/ monthly service charge so only need to buy contents insurance for your belongings.
You won't need a survey for yourself as the Shared Ownership company will own the building, but your mortgage company might require one.
The valuation may be done by a charted surveyor and the sale price is fixed, unlike an ordinary sale where the seller markets at a price based on an estate agent estimate that you can make an offer on.
Check that your mortgage company will lend on your Shared Ownership scheme. Check also that your Solicitor/ Conveyancer will do this work as it involves 3 parties - seller, Shared Ownership company and you. This may then incur additional costs as you are paying for their time.
Stamp duty is a tax levied on the total value of the house. So if your £100,000 is e.g. a 50% share of a house worth £200,000 then that would attract Stamp duty. However, if everyone buying is a first-time buyer you would be exempt.
Check what arrangements there are for staircasing (buying more shares), e.g. what multiples, how soon, what maximum, how many times. The more you buy, the less rent you pay, buy more mortgage if you don't use savings. Is there a certain percentage where you no longer pay rent (mine is 75%). If you reach 100% will you own the freehold?
Check also what the arrangements are for selling. The property may have to be offered back to the Shared Ownership company for a period of time before you can sell on the open market, which would delay an onward purchase, or you may have to pay the whole year's service charge for instance.
Expect the whole purchase to take longer than for an equivalent house purchase. The Shared Ownership company does not have the incentive of a private seller to get on and move fast. You may need to chase.
Buy plenty of wine!