If you wish to make curries across the entire BIR range I think you should try another base rather than Darth's. It was ideally suited to the hotter curries he liked.
As UF said the Taz base and the CA base are good but no better than many on here. The Taz base is great for those new to BIR cooking as there is minimal chance of burning the spices which will ruin any curry dish. Stephen Lindsay has done a lot of work on developing and adapting existing recipes specifically for use with the Taz base.
One base definitely worth making is Chewy Tikka's 3 hour base (total time from start to finish). CT has done many excellent instructional videos to accompany this. Again, a real bonus for anybody just starting out on the BIR journey.
My personal preference (and a few others) is the Zaal base shown to the "Fleet 5" by chef Az back in Feb this year.
And another base which is beginning to attract attention and receive good reviews is the Little India base courtesy of Curry Barking Mad.
None of the above mentioned require the use of a pressure cooker, although CT's base can be cooked using one and there is a video to help.
Let us know which you decide on and the results as they come in
