Germinating Cactus Seeds - few q's

Hi everyone, spring time again
I've bought a bunch of seeds to grow this season - can't wait to plant them but before I do, I'd like to ask some questions.

Here are the seeds I have with me now:
-Lithops (various, some of the easier species to grow)
-Astrophytum capricorne
-Astro myriostigma (various forms)
-Astro asterias
-Tricho pachanoi
-Lophophora williamsii

I've grown some succulents from seed before but from what I see cacti are a bit different - they seem to like warmer temperatures to germinate (understandably) as well as a rockier medium.
I've bought a bag of propagating sand because the sand I used last time was too fine - this seems suitable. I've also heard that it's better to sieve out the larger stuff and only use that? I tried that with a pod of golden barrels a few months ago just to try it out, and while a lot of them germinated, they didn't last very long - it seemed they couldn't really get a grip in the rocky material and the gaps between the pieces was too large... I'm not sure if I should really be sieving out the smaller pieces because of this.
I've also thought about mixing in a bit of soil (I've got a light, fine seed raising mix) which could help fill in the gaps... and I also see that some mature cacti are planted some sort of crushed scoria, but I haven't heard of anyone propagating seedlings in this so it might only be suitable for larger plants.

I'm also wondering if a heat mat is necessary or beneficial at the moment - while I have germinated some agave attenuatas quite successfully with no extra heating, I'm wondering if these seedlings will benefit from extra heat while germinating, especially since it can be controlled and kept quite constant. I do have one, so it's always an option if there's some benefit to it, even in spring.

(what's this emoticon meant to show anyway..)

Thanks everyone!

Hmmmm..... I cant answer any of your question, However an old eskimo seaweed planter once told me this ....."He who listens with one ear, Only see's half the truth" I think this is his legacy.

That or cyclops are just downright cool and are not acctually huge but tiny little dudes with clubs that ride ants and hang around your cactus. They farm mealybugs for a living and smite those who oppose them.

Im looking foward to hearing the answers to your questions as I've been asking myself similar ones. another I was curious on is if your using artificial lights who long should you be pumping the light? 12hrs?

-A

18 hours mate straight to an artificial summer lol....i am wondering who else soaks their seeds? as i have , with better results than not soaking, but am sowing so many this year that dont know if its worth the extra hassle

blowng
I think soaking works well for cactus seeds with hard shell. I soak Echinocactus horizonthalonius seeds in warm water. This soaking give me a quite good germanation ratio.
Hanzono

I have found that most cacti get better germination with a 12 to 24hr soak in weak seasol before planting. I suspect that its the soak rather than the seasol that works, placebo effect - makes me feel better.

12hr light for spring plantings works for me, i dont believe that sudden changes in photo period do seedlings any good. so i only use artificial lights until midsummer, then they stay off till next season.

i just use standard media sieved for the seeds, that way when i eventually get around to potting on they dont get a shock. i dont think its nessesary for most seedlings just the ones i REALY dont want to kill. + i dont want to be holding any more potting media's than i allready do.