I would recommend a dichroic head (preferably 4x5).
Commercial grade 4x5 dichroic enlargers are going for 10 cents on the dollar of their original cost, in many cases free, leaving plenty of spare $$ for some good glass.

As for the dichroic filters, they are very stable; not so for the gel. The added advantage of going with a dichroic 4x5 right out of the gate is that you have all of the primary format sizes covered, as well as the option to print color.