Like andibig said, formula is still more important than solids, and it will be for several more months. At his age, he should be getting at least 32 oz of formula per day. Formula is much more filling than solids, and if his bottle intake has dropped a bit in favor of solids, I'd guess that's why he's waking up hungry at night. He might also be waking more from gas, which is really common when first starting solids. Shoot for 32 oz per day, maybe more since he was a hungry boy before, and guesstimate how much solids he should be getting from there.
As for timing, it really depends on what works for you and your LO. Lots of moms give bottle first then solids after to make sure baby fills up on the good stuff. Some give solids right after, some wait 1 hr, some wait 2. It just depends on naps and what works for you. Some moms can give solids first and not see a drop in formula intake...never worked for me!
It's quite possible to overfeed, especially if your LO isn't getting enough formula. New solids eaters, especially younger babies like yours, often don't know how to tell you when they're full. The feeling of solids in their tummies is different from formula, so it's a different full feeling, KWIM? Also, it can take time to learn how to tell you once they do know what full feels like.
Hope that sheds some light!