Hi again,
Never count hours required as hours needed. If 10 hours are required he may very well do it in that time as he's young and probably learns fast, but it's no guarantee. Hours stated are minimums and often more are needed to reach the required standard.
Yes you can use LAA aircraft for hour building even though they are Annexe 2 not EASA.
Shares work easily enough. An aircraft is owned equally by say four people. When one owner sells their share, the new owner (assuming approved by the other owners) pays the asking price then pays a quarter of the fixed costs such as insurance and hangarage. The group will have worked out an hourly rate (either wet or dry of fuel) and that is paid for hours flown. Most groups have rules requiring minimum hours though, and possibly tailwheel differences (as most LAA shares are in taildraggers) ... Motorgliders are taildraggers - so no problem for him (his lack of hours might be a problem). If buying outright, I would make sure you find a good local LAA inspector to find a good one and go for a single seater. You can pick one up under £5K and the costs/risk will be less than a two seater.
SS