Hi @Domi79 , I was in a situation similar to yours some years back and I have a few thoughts.
First, I would go systematically through Grade 3, just following the Beginner’s course. At the same time, you could also do some “extra-curricular” blues study. There are a number of specific blues lessons in Grades 1-3 (maybe only 2-3), that you can check out. Just skim through all the lessons to find them (the search engine will give you too many hits for “blues” to be useful).
EDIT: I just noticed that Module 13 in Grade 2 is fully dedicated to the blues. You may know this stuff already, but check it out in case you don’t.
There is also a Grade 4 module “Blues Studies”, that has 4 blues lessons, which you could check out. (I quite liked these).
Then, if you want to keep going with the blues, there are a couple of ways to proceed. At this point, you might want to decide if you want to pursue solo acoustic blues (think Bill Broonzy or Lightnin Hopkins) or electric blues (BB, Freddie and Albert King, e.g.). They are quite different, of course. Solo acoustic is designed to basically get you playing blues instrumentals by yourself on acoustic guitar. Electric blues teaches rhythm and lead playing that would take place in a band context, typically.
If solo acoustic is appealing, you could check out the new Solo Acoustic Blues course (it’s paid). The first few lessons are free and can be found here:
https://www.justinguitar.com/classes/solo-blues-with-matchmysound-solo-blues
You will see from these free lessons if this interests you and if you are at the right level. Some experience with fingerstyle playing is required, I would say.
If you want to pursue the electric path, BLIM would be the way to go (so I understand, I haven’t taken it). In the meantime, you could also check out the Essential Blues Lead module in Grade 4:
https://www.justinguitar.com/modules/essential-blues-lead-guitar
and the blues rhythm module in Grade 6:
https://www.justinguitar.com/modules/essential-blues-rhythm
(One final caveat in what I’ve written here: most things can be played on either electric or acoustic guitar. Some people play the acoustic blues stuff on electric (though it sounds better on acoustic!
) and you can play much (but certainly not all) of the electric stuff on an acoustic. )