Plastic bottle question

I have about 3 cases of brown 500ml plastic bottles that i got from a brew on premise before i got into homebrewing.

I'm ready soon to bottle my first batch so the question is...

How long will the beer keep in thse bottles? I'm told if you store them on their sides they will last longer, is this true?

I'd like to be able to keep 6 or 12 from this first batch for a few months to see how it ages. Will these bottles be ok for that?

Out of curiosity, are the bottles marked for recycling by #1 or #2? There has been some controversy regarding the health effects of plastic food and beverage containers, particularly certain types. I discovered that several of my Rubbermaid drinking water containers that I have been using for years are made from #3 polyvinylchloride, which is potentially one of the worst offenders.

Another consideration regarding bottling into plastic is oxygenation of your brew. I would suspect that the type of plastic and the wall thickness could affect this.

I don't see how oxygenation is possible with a container that is under a positive pressure such as a bottle of beer. To me that defies logic. Can someone please explain how that is possible?

I've been using 2 liter plastic soda bottles for over three years and have never encountered this. Have I just been lucky?

That's a good question. Apparently PET allows diffusion of oxygen through the container wall.

BOP bottles should be PET and should be just fine. You may want to get fresh lids to make sure they seal properly. Store them upright. This will keep the sediment on the bottom where it belongs and there is no need to worry about the cap drying out which is why you store wine bottles on their side.

I have re-used 2 litre soda bottles for many a different beer/cider/mead and have many that have aged for over 6 months to a year with no sign of lost pressure, or oxygenation.
Take it for what it's worth, I have a few that I think I will be ageing meads in for around 2 years. Should be an interesting test.