I don't see the lsys license option listed on any of the reseller websites as an option. So I suspect this is not available on this platform.
lsys is available on SRX4600. SKU's for LSYS: SRX4600-LSYS-X where X is 1, 5 or 25. Licenses are stackable so if you need 50, you order 2 x 25.
Regarding scaling I don't think I'm allowed to post scaling targets on this public forum but it's higher than 100.
Scaling also largely depends on the features enabled per logical system... to validate scaling please reach out to your local Juniper account team which should be able to help you qualify how high you can expect to go.