That's a great hint with last posts page! I've missed it somehow. I already see that it will improve speed and reduce overload significantly.
As for talking - I don't have this thing 100% ready yet, so I don't know how much load it will generate. Not enough info for reasonable queries to admins yet. But you are probably right - I should start talking beforehand.
Haha thanks for the gesture already !
Well I think you need to poll every registered user once every couple of minutes to check if the user has a new post, I don't even think you need the real thread as the single post contains info on the tip (for who is it and how much is it). But if you want to check once every 5 minutes and 1000 users are registered you are hammering the forum with more than 3 requests every second for 24/7. For 10k users that would be more than 30 requests per second.
If it scales you could try some tricks like trying to predict when which users will post new posts based on their stats page (and time settings).
Of course it will take some time before 1000 users have registered. But if you talk with the mods they can also let you know in advance when the forum layout changes so that your scraper / parser won't break when this happens all of a sudden (the bot cannot screw up with sending tips with wrong amounts / to wrong person imo).