It needs not be a broker plugin, it can be any DLL. If it is a broker plugin and you have a callback function in the script, you can use BrokerProgress(ptr) for transmitting information. Look for the description in the manual under "Broker Plugin". An example of such a callback function can be found on the HFT page. What it returns is up to your implementation.

There are no T6 structs at runtime, T6 is only used for historical data. Still you can set the prices and spread directly, either with priceQuote, or with priceSet. As you can imagine, this is pioneer area, AFAIK priceQuote has so far only been used for HFT simulation. When you encounter problems, you know the procedure: email Support and you'll get help.