Money making tips

Hey all! I want to make as much money as possible to decorate and expand my bakery, I hear things like spamming red velvet cakes is a good money maker but I would love to know about appliances. Are the standard ovens the best thing to get? Are there other appliances that have better recipes? And is it worth spending gems on expansions or more ovens? At the moment it is 40 gems per expansion.

TIA!!