From what sources will exchange rates be taken?
The wallet is going to work with the top 100 CMC coins. So it would be logical that the price of these coins also coincided with this resource
This assumption. I would like to know what the developers will say. It should be remembered that CMC shows average prices. In addition, sometimes prices are incorrect.
Probably it should be described in white paper, but I could not find it. Does the team have technical documentation?
But even without this, most likely they will be based on data of CoinMarketCap, he really sometimes shows not the exact prices for the crypto currency, like yesterday with bitcoin.