I didn't have the option of retaining the glass in mine,it was full of bullet holes!
I realise to replace your windshield and large rear glass is a somewhat more expensive option than the older flat glass models,but personally I would fit your old glass,with new seals to git 'er done,then save up the $$$ and replace them as and when funds allow.New glass really does make a difference to the overall look.
Replacing them later should have no ill effect on your finished paint job or new seals,if that's your concern.
Unless your planning to show your truck,I wouldn't worry about it too much.
