Firstly, welcome Lee to the curry journey ;D . Re. spices, see if you can find a local asian general store or wholesaler. They normally all the essentials, it's fresher and cheaper. Had you picked Chewytikkas base and spice mix, you'd be having far less "angst" with equally as good results IMHO ;D.
Back to your questions. Ground cardamom is a bit of a rare beast, probably because there is little call for it. Just a CA quirk, although some would say it does add something. I didn't notice any earth moving impact when i used it in his mix powder. Next best thing, deseed the pods and grind it using a pestle and mortar or a cheap coffee grinder which can be used for spice grinding, if you feel the need. The only time i use mine is to make up garam masala, and that is not very often. Handy to have if you want to try grinding whole spices and using freshly ground. Not likely in BIR cooking, other than for garam masala though.
As for the tomatoes, simply chop them and throw them in. You will be suprised what a good job your stick blender will do. Just make sure you let it rest frequently. Personally I use a jug blender and have been using the same one for bases for the last 20 years and it hasn't failed me yet. As for sieving the base, this used to be done in byegone days according to CT and some members on here do it. I never have. I suppose it produces a much smoother sauce with no chance of any small fibrous material being left in the base. Whilst i can appreciate the reasoning, providing you blend thoroughly, the impact it will have on the overall flavour of your curry will be absolutely negligible IMO.
The main thing though, enjoy what you're doing. Keep walking for a while before you start to run. I'm sure you'll soon be producing quality curries. Like most things, it takes time and plenty of practice. Watch the videos from Currybarkingmad and Chewytikka, learn the sequence and practice the technique which is half the battle i believe.
Feel free to ask as many questions as you want, no matter how trivial they may seem. There's always someone on here who will be willing to help. But you do have to make allowance for our differences of opinion occasionally.
Keep us posted on how the curry goes
