Welcome to RPM, Tom.

People will have lots of ideas for you...although you seem to be
thinking things through by yourself. Most of us remember our first
efforts at a pond (and our first anxious post on rpm or rec.ponds.
There are a number of ways to build above ground or partially above
ground ponds with liners.

By all means think about your filter process as well. Many of us use
smaller 'veggie filters' as easy, low maintenance filters (10% or more
the surface of the larger pond, filled with plants ans slow flowing
water to help settlement of gunk. Water drawn from the low point of
the main pond).

By all means launch any questions you may have. Folk here are always
glad to share their best observations (and to air their differing
opinions).

You are welcome!

Jim