Italian Meringue Buttercream the firmest ?
I live in the tropics and room temp here is hot,
is Italian Meringue Buttercream the firmest, nonmelting kind ?
Also can someone point me to a recipe using weights as opposed to
numbers of eggs etc ?
Definitely not. IMBC and SMBC are both very heat-sensitive and temperamental.
There's really no such thing as a non-melting icing, but an American buttercream made with shortening instead of butter is going to be your best bet. Not your tastiest option, but it'll have some hope of holding up.
Visit www.cakecentral.com for a wealth of information on making and decorating cakes. I know there are some great decorators from the tropics on that forum who would be able to give you the best guidance.