Whoa! Nice pond indeed! You have really been busy!
One thing about cement is it
can affect the PH of your water. Putting your plastic liner over the top of the cement will keep this from happening but I would say that if you put sand down first and you are careful when you are in your pond, (for cleaning or for cooling off)
you should be fine just like it is! About the evaporation. In the dry heat that you have there, I can imagine you will have much evaporation. Maybe an inch or two a day wouldn't be unusual. If it is much more than that, I would check for leaks. My small pond evaporates about an inch every two days or so. As for the
plants, I am always trying new things and have found out that many
plants that are not traditional "aquatic"
plants will grow well in water. I have put 'creeping jenny', 'forget me nots', several types of ivy and mint family
plants and I have had very good luck with wild strawberry
growing in my small pond! I actually had some tiny berries on one of the
plants. You have to do a little research tho because there are some
plants that are "toxic" and can quickly foul your water and/or kill your fish. I looked at the
plants you have pictured and one of them looks a lot like a type of mint. I would experiment a bit and dig a small
plant up, make sure and get 'all' the roots. Rinse the roots gently with pond water in a bucket and put the roots in a small jar filled with pond water and put the jar in the pond with the lip of the jar just under the surface of the water. Every other day, pour the water out of the jar and replace with fresh pond water. If after two weeks or so you do not see any major rot or death of the
plant or roots, you may then pot it in loose gravel in a pot and set it in your pond! Again,
GREAT JOB
on digging your pond and keep us updated with pictures!
(its not expensive here anyways) so give me comments on wat u think, personally i prefer a cement one for it wont tear up or anything...
and i hope to take out the plastic and fill it wil cement, coz i thinks its going to be easy to maintain...thnx again for ur help!!, ill keep posting pictures 
anyways...ill keep u updated!!! :thumbups: talk to u later!