use you axis and allies pieces and buy Table tactics central powers set.
Also, goto www.scalespecialties.com and look for navwar for the zeppelins
They have armored cars and tanks too if you want metals.
If you want real ww1 infantry, buy 1/72 scale hat/ airfix ( see toy soldier review. com for pictures. They have cavalry too
For real ww1 planes goto www.brookhurst hobbies.com look tumbling dice vapor trails 1/700 scale planes
The entire set would be about $150 for all nations. The game has been played hundreds of times over the years. Its gone thru alot of playtesting so you will find it probably better than Axis and Allies.