liquid cultures really are awesome. once you have LC you can innoculate grains and it speeds up the process a lot, plus success rates are very high. For LC make sure you use a sugar that does not caramelize. I.e. dextrose and malt work well; honey should work and works but not quite as good.

For gas exchange I always used several layers of protection - you want the jar to be able to breathe but you don't want dirt or bacterias etc. to get in. I used tyvek envelopes cut up to fit below the lid of my jars as the first and most fine-layer. In the lid there would be at least one hole filled with polyfill through which you can inject or use a self-healing injection port made of silicone (I've used bathroom silicone and it worked just fine for one round of PC, the second time I'd use it it would start to deteriorate, so renew every time you re-use the jar). Over the lid I put a coffee filter to keep out dust and stuff falling onto it. It's a bit overkill, but I'm rather safe than sorry with this kind of stuff.

For preparing grains this tek: Shroomery - From syringe to print using rye is really good. you can use it for WBS as well. There's also a lot of useful information here: http://fet.ezin.cz/files/roger_rabbit-mushroom_cultivation.pdf though it reads quite choppy. RR says tyvek should be on the outside of the metal lid (using two piece lids of mason jars) but I've had good results with one-piece lids and putting the tyvek on the inside and the polyfill etc. described above and never had a single contamination.

Hope you have fun with your grows!