The idea is to pin it only temporarily until it is established well enough to stand on its own merits. To that end a USD+EUR basket is adequate, but honestly, the specific basket doesn't matter: ANY reserve currency is a couple orders of magnitude more stable than Bitcoin has been.
The strength of pinning will be adjusted as the number of coins in circulation increases. For example, it will aggressively pin until the market cap is $1B; become gradually more conservative with adjustments from there; tapering down to zero pinning once the coin supply reaches $1T. After that it gets to float.
Again, your system is too open to uncertainties and not practical to implement.
And even supposing it was possible (its not), Bitcoin has changed price a lot mainly because its a very small market. Trying to adjust inlation because of some exchage rate wont change it too much. Any big influx of money will make it go up and any big sell off will make it go down quick. As Bitcoin grows this will disappear.
Take a look at any fiat currency. People trust them pretty well even when central banks are fooling around with them.
Who's going to trust Bitcoin when it can't hold value within an order of magnitude for 6 months at a time?
Fiat currencies are not "trusted", fiat currencies are accepted because the government impose them. If the governments were ot forcing their fiat currencies nobody would accept them.
And there is lot of people trusting bitcoins (including me).