Like I said, download the spreadsheet and play with it. You can port the RS100s to reach 70Hz.
Line Arrays are a compromise, like any other speaker. They will have varying freq response based on distance, and will lobe unless power shaded (again, check the spreadsheet, you an play with power shading as well with it).
The BFM TLAH is a value speaker, IMO. It will get you lots of the way there for very little $$. But if you are looking at drivers in the RS class, you may have a budget that may mean you can forsake the value that the TLAH is for something better. If budget is an option, BFM speakers are not bad. But they use several different drivers, and a generic crossover, and will generally need EQ to sound best.
If you are looking to spend over a year testing and optimizing, by all means, start your own line array design. But at least one has already mentioned Selah Audio. They have been doing arrays for a long time. Budget is pricey, though.