Use a mixture of mild and hot varieties of red chilli like Guntur(hot) and Byadagi (mild). Read more notes on this in Bisibelebath recipe
AVOID dry roasting all ingredients together as it results in uneven roasting or burning of ingredients.
If you wish to make a smaller batch, a 4:1 ratio should work well between coriander seeds and cumin, fenugreek and black pepper. Adjust proportions for the other ingredients accordingly.
Avoid dry roasting red chillies (without oil) or they'll emanate pungent, choking fumes. If you feel the spice mix turned out to be short of red chillies or doesn't taste hot enough, you can always adjust by roasting some extra chillies, grind to a fine powder and grind again together with the mix to get it all mixed well.
If you use the powder sparingly, consider storing it in the freezer. That way, the spice mix will retain all of its flavor without tasting like wood husk.
SSP brand hing is available in Bangalore - Mysore areas as far as I know. LG brand is available even in the US.
Chana dal or any dal is not used as the mix tends to spoil faster.