Hi.. I from Denmark, so I can't say that my experience will necessarily mean that you'll have the same, but I can at least share it.
I've had League Pass since 2008, and as others have noted, it has indeed gotten much more expensive since then. However, the quality in the product has also increased, so I will not complain. In Denmark there is only one game broadcast per week, which is the Sunday matinee game. In the cases that the Celtics have been playing those, I have never occured a blackout, although I am positive that the channel has the rights. This applies to e.g. the all-star event, playoff games as well.
In any case, I'm positive that you'll be able to stream the games after the blackout. But, again, my experience is that the blackouts are warned, but I have never actually experienced them myself.
And, usually there's a 14 days trial right around the start of the season. The length and quality of this may change, and as far as I remember, it's probably announced pretty late. If you want to be safe, just buy the month-to-month subscription, but otherwise, I'd go for the full package right away - that's what I've done!