Is linking necessary to download files?

I recommend working through the tutorial to see how to call methods in that SDK. For example:

[self.restClient loadMetadata:@"/"];

So, using loadAccountInfo would look something like:

[self.restClient loadAccountInfo];

And you'd need to implement these delegate methods to get the response:

- (void)restClient:(DBRestClient*)client loadedAccountInfo:(DBAccountInfo*)info;
- (void)restClient:(DBRestClient*)client loadAccountInfoFailedWithError:(NSError*)error; 

The App Console only lets you generate an OAuth 2 access token, so that wouldn't suit your needs, as you need an OAuth 1 access token. You can get that by implementing the app authorization flow per the tutorial just to use for your account, and then pulling the access token out using DBSession.credentialStoreForUserId. (Again though, I should emphasize that this is not a recommended way of using the API, which is why this isn't particularly easy. If you just need to distribute content to the users of your app, a CDN might be a better solution.)