P.N.
The first few months of solids is really a lot of experimentation for the baby, rather than eating for nutrition. They don't get the bulk of their nutrition from solids those first few months, and they don't need to.
Always breastfeed first then offer solids. Before a year solids really shouldn't be replacing breastmilk. If you feed solids first, he may fill up on food that is far less nutritious than breastmilk and that would affect supply. If you breastfeed first, he will still have the fun and learning of eating, but it is less likely to replace breastmilk that way.
You also may consider rather than spoon feeding purees allowing him to self feed. We started solids later (almost 10 mos) and never spoon fed (we did it for allergy reasons, not supply issues).
Kellymom has a lot of info on starting solids. http://www.kellymom.com/nutrition/solids/ready-solids-lin...