Surf-boat showing exotic fish - there! (6) ?ASULA
Old writer's plunge scatters untold liquid, but not all (6) SO?SSE is I think sousse a variant of souse but the rest is obscure
Shakespearean king not entirely without support in due course (6) ?LONSO is I guess all so from alon(e) + so. Is it ok to assume so can mean in due course?
1. MASU (a Japanese salmon) + LA! (look! there!) = MASULA (a surf-boat)
2. SOWS (scatters) + SE(a) (untold liquid, but not all) = SOWSSE (old word for plunge)
3. Yes, Chambers gives SO as 'in due course, thereupon, thereafter'