Hi Emin-J,
I have tried making base sauce for the past 2 years and still maintain that I make a better curry from scratch.
I also attended an Indian Cookery Course at The Safron House - Rickmansworth earlier on in the year, where we did similar stuff, the spice trail etc and more importantly the medicinal purposes of spices too. The chef that taught us had a masters in Food science, so she really knew her stuff. We went on to produce Garam Masala, a fantastic "Chicken Chilli Marinade" and there were 4 of us on the course and a slight increase or decrease of any spice produced a completely different flavour as we all tried each others. Some were hotter, or had more ginger or garlic etc.....
We also did a fish masala marinade and one for paneer, we made Riatu (fresh yougurt & cucumber dip), The original Bombay potatoes, Vegetable samosas, Vegetable Bhajis (I've posted the recipe on here), they were fantastic and vegetable pakoras.
We then marinaded the Chicken and fish with our marinades and left them to "fester" as it were for about an hour then cooked them. The food was real quality Indian food and not a base in sight.
So all in all pretty much a day like yours. They hold a second day which I will book when I can afford it based on main courses

I highly recommend these cookery courses to anyone here, they give you such an in depth knowledge of spices etc.......