Seeds should stay viable as long as they are stored cold and dry. I would sow the nidiformis, burmannii and indica now. Germination may be a little slow this time of year, so be patient. If you can get the petiolaris hot, and maintain the heat at night, I see no reson not to try this as well. The only seeds I do not sow in colder months are the North American temperate species, since they are photoperiod oriented.
Here is how I do it:
Have your moistened mix in the pots and ready. Take a sheet of white paper and fold it. Good bright light is needed to see the seed. Put your seed on the paper, and by gently tapping, try to roll individual seeds down the fold, and onto the medium, one by one. Don't sow too thickly: although the seeds are small each one is a potential plant. 25-30 seeds is a good sowing, and this is not much when you see it on the paper. Seedlings grow best when not overcrowded. Keep the end of the fold moving, so that you plant each seed in a different place
What you want for mix is a fairly loose medium for the small roots to penetrate, which is why I recommend peat/silica sand 50/50. The sand and preferably the peat should be rinsed to remove micronutrients that wil favor algal growth. I put the sand in a bucket, and add rain water, swish it around until the water looks clear. (I generally do not rinse my peat, I have it in an outdoor bin where the rain leaches through it all summer, so I have no method) If you plan on transplanting after the seedlings develop a little, then pure peat is an option, as is milled dead sphagnum moss. Both these substrates have natural antiseptic qualities, and they also discourage fungus and algae. Algae can interfere with germination, and competes with the seedlings. You should however aim at getting them into their permanent homes in a good 50/50 mix as stated after they form 4-5 leaves. Remember to be patient: seed can take awhile to germinate, usually in about 2 weeks to a month you should see some results. Don't water or spray from the top as this can bury the seed. Use only rain or better, distilled, water. Give it warmth, but light levels should not be high until there is germination: too much light will encourage algal growth, the main enemy of seedlings. Check the pots weekly (or daily
, and when you can see germination, move the pots into good bright light, no direct sun. Humidity should be reduced in stages, slowly, after germination. If the pots are in baggies (which I recommend, seed needs high humidity to germinate), poke a hole or two after you are sure all the seed has germinated. Then in a week a couple of more. Ideally you will be able to do away with the cover in a month or so. Be attentive to what the seedlings tell you, but expect some to die off in the process. The survivors will be adapted to harsher conditions, and will be healthier than plants grown in too high a humidity. 70% is about ideal for most of these plants. It is fascinating to watch the growth process, and I consider growing from seed to be one of the finest aspects of this hobby. Enjoy!