are you planning on turning it possibly into a natural swimming environment, or is it a pool that you are looking to utilise as a pond with fish?
If a pond with fish, then rather create a trickle\bakkie shower type filter instead.....it's the best kind of filtration you can get. Plants often carry horror stories with them, where the plants can harbour unwanted bacteria which is often difficult to eradicate as they have difficult to reach breeding areas etc. This in turn creates an unhealthy environment and sick fish. Also when medicating a pond with plants you need to be careful as most of the medication used can destroy the plant life, like salt for instance.
If purely a natural swimming environment then plants is fine, dont know much about this.
However, for plastic containers etc, phone someone like pioneer plastics, they have an online brochure that you can enquire on for prices etc.
They are in Pretoria, not sure where you are from?
www.pioneerplastics.co.za