btw what is the level of ur coach??
i think if ur one is not 'solid' one...
u may choose to get a solid/poor...
or buy coach-seed to transform them later...
i suggest upgrading stadium should be done mostly in between seasons...
because usually this will have 2-4 weeks gap...
then u can wait prize money/season ticket/etc incomes to get more cash...
and upgrade at last moment...
so prevent waste of arena cost...