using kefir 'grains' will produce a much more powerful end-product, vs using the starter that comes in the sachets. The stuff in the sachets tends to be a proprietary culture, and won't contain as diverse a selection of beneficial yeasts / bacteria.

it might be worth seeing if you can get your hands on some grains. there's usually somebody in the local area who will have them. failing that, ebay is good.

as far as lumps go, I usually give it a good mix with a wooden spoon, before straining. that helps to leave you with a much more consistent product. 👍