here's what I've done in the past when I had to brew on the cheap, or had to improvise supplies

1. air traps are partly there to keep airborne "bad stuff" out, and to mainly allow CO2 to escape, balloons are used because they're cheap, but don't affect the outcome of the brew, the pruno made in jails doesn't taste bad because of the balloons, it tastes bad because its made in jails from bread yeast and orange juice, crappy ingredients, crappy brew

but something as simple as cheese cloth stuffed in the mouth of the container would work, Lambic beers are made basically open to the elements, but if you want a little more protection use a length of plastic tubing with either a rubber stopper or a handful of rubberbands around one end so it fits tight in the bottle, and enough length so the other end of the tube hangs below the first end, but outside the bottle, and stuff a piece of cottonball in that end to act as a filter and to keep bugs from crawling up the tube (spiders especially have a habit of doing this)

just about anything that will let CO2 out, and keep airborne bacteria, yeast, dust, and bugs out works fine, even old shirts as cut into rags and rubberbanded them over the opening would work


2. if your doing cider champagne yeast will work fine, had good results before, along with equally bad results

if you have any local breweries around, microbrews or even large family "been in the city for 100 years" breweries, just not super mass produced factories where everything ends up in cans, just go in and buy a bottle, especially if they prime in the bottle (small layer of trub on the bottom of the bottle is telltale dead or inactive yeast, this is what you want to see), otherwise take a tour, ask to talk to their brewmeister, and ask for a sample of the yeast or an unfiltered beer, tell them you brew at home and you have a hard time finding yeast, you'd be surprised how happily most brewmeisters will be to give you free beer supplies, for years I never bought yeast, there are so many breweries around me I'd just ask, most of those guys started brewing beer because of the same reason I did, so they tend to like to be a mentor of sorts, only a mentor with a several thousand gallon steel brew vessle

otherwise buy online, but don't use bread yeast, its bred (no pun intended) to produce VOLUMES of CO2, but little to no ethanol, and produces a poor tasting, thin, "bready" tasting brew


3. I honestly haven't used mine in years, I don't really care how strong it is anymore, you just know when its done brewing when the bubbles stop


4. depends on the plastic, plastic can be hard to sanitize, and can pickup and hold odd flavors, so try and stick to glass
wine bottles, cider jugs, old glass milk bottles, even seen "brewed in the bottle" beers using old corona bottles (wouldn't recommend it though)


I still use 1 gallon glass apple cider bottles for small batches, sometimes even reintroducing the original cider back to them to ferment into "proper" cider, instead of just thick apple juice, I have a handful of large rubber corks with holes in the center and a plastic tube stuck through for my airlock, very rarely have bad batches with them anymore, I wash the bottles all with a strong water bleach mix, and steam the stoppers, tubes and bottles before use

Although glass is classier, I have had no problems using food grade plastic buckets for brewing. I also use plastic water cooler jugs but I have a carboy brush for cleaning them which you pretty much need.