If I spend these story points would that preclude taking a season in Gaelic for 8 points? How will this interact with points from the meeting which is an 'adventure' in the same season?
It doesn't. Per the house rules, adventure xp don't negate your normal seasonal advancement; you can adventure and still get full benefit from studying a summa, for example (barring penalties for lost time). And the prelude threads are kind of pre-Spring-1220, so it's kind of all over the place, so don't worry about doubling up on this one.
Noting that Independent Study gives +3 XP from adventures, I will put 5 into area Lore: Loch Ness Covenant and 1 into organization Lore:Loch Ness Covenant.
If Arthur also gets 3 xp he will put them into area lore:Loch Ness Covenant
The lad only had one line in the thread, so he doesn't.