Regarding your plan, a half-fare card looks cheapest:
The card costs 120 CHF, and every ticket will be half-price after that:
- GVA Airport - Wilderswil 38 CHF
Excursions in the Jungfrau region:
- Schynige Platte 32 CHF / worth it for you since it starts from Wilderswil!
- Schilthorn ~65 CHF / better than Jungfraujoch for most
- Wilderswil -> Basel 32 CHF
Total cost approx 290 CHF.
BUT a 4-day Swiss travel pass might be more convenient since you won't need tickets except for mountain railways.
- 281 CHF for the pass
- about 50 extra for Schilthorn
and if you happen to schedule, say, a day trip to Bern if the weather is bad, it will be included.
You'll have to decide whether the convenience is worth a potentially higher price.
You need a separate TGV ticket from Basel to Paris: buy on SNCF, prices vary wildly, the sooner the better.