There's lots of varying information out there about solids. You really don't need to start with cereal and many people choose not to (baby rice has little nutritional value so if you do choose cereal I would personally choose something else), there are newer guides now that advise to begin with iron rich foods such as meat. It's also advised to avoid wheat until 6 months which you might like to take into account as your LO is still a little under this age.
As for how much, it is really down to you and baby. Your baby will let you know he has had enough by closing his mouth, turning his head or batting food away, or throwing it to the floor if he is self feeding. He'll let you know when to stop offering solids. Also you can monitor is daily milk intake to ensure it stays up as milk (either breast milk or formula) is still his primary food. If his milk intake remains healthy there is no problem him taking lots of solids, if his milk intake drops too much or rapidly then cut back on the solids.
(the number of teeth has no bearing on how much or what sort of solids you can feed. Babies with no teeth can gum on foods such as meat, steamed vegetable batons etc)
hope this helps
