SMS Spam invoked by iOS only for following scenarios If above conditions are not satisfied, program will not be invoked and your filters won't have any effect.
No. Filtering is sender based. Once a sender is blocked it will stay blocked unless you add sender to your contact list or reply to sender at least 3 times. If message is once accepted, all other messages from that sender won't be filtered. This is the way Apple programmed it.
Filters are called according to following order
Try one of the followings
Go to Settings tab and click Test Filters. You can easily see what is happening under the hood for given SMS.
No. Filtering happens on your device. There is no way for filtering extension to write data. It is forbidden by Apple. Although Apple allows using a web service for filtering, this application only uses local rules for filtering. What happens on your device stays on your device. We don't store, transmit any data about your SMS, period.
No. This program doesn't collect or transmit any sort of data including statistics. Besides this online help page, this program doesn't use internet at all.
If you want to block by word, you can add a Regex rule. For example if you want to filter go but not going add a following rule to your Black List.

Content: \bgo\b
Rule target: Message
Rule Type:Regex.

You can create pretty complex rules with Regex. Please search Regular Expression with search engines to learn more about it.
You can use Regex for this. If you want to filter all senders who has 4 digits number, add following rule to your Black List.

Content: ^\d{4}$
Rule Target:Sender
Rule Type:Regex.