Learn Danish: Det er vores ide.

No! Unlike the words for my (min/mit/mine) or your (din/dit/dine), the word vores (our) never changes. Whether the noun is an en-word, an et-word, or plural, it is always vores.

Since idea is an en-word (en ide), shouldn't the sentence start with den instead of det?

When you introduce what something is using 'It is...' or 'That is...', you always start with the neutral det er. You are pointing at a general concept before specifying what it is, so det works as a generic 'it' or 'that' regardless of the noun's gender.

I sometimes see idea written as idé. Is ide also correct?

Yes, both ide and idé are completely correct in Danish and mean the same thing. The accent mark over the 'e' just shows where the emphasis goes when speaking, but you can safely write it without the accent.

How do you pronounce vores?

It sounds a bit like 'vo-us' in English. The 'r' in vores is a soft, vowel-like sound that blends right into the 'e', so you don't pronounce a hard English 'r' at all.