Emma, it sounds like you are doing a great job. There is really no rule book on solids - it's as much a matter of trial and error as anything else. Every baby is different - some eat more and some less.

It also depends on whether he is breastfed or formula fed (or a mix). Breastfed babies get plenty of iron from breastmilk, so their iron stores are usually fine until around 12 months. With any baby, it is important that the solids don't replace milk, as milk is the main source of nutrition until 12 months. This is especially important with breastfed babies as replacing breastmilk with solids usually will lower the baby's iron levels.

Rice cereal is really only useful to get the baby used to the texture of food and the idea of eating. It doesn't contain any real nutrition. You can go down the path of introducing pureed vegies and fruit now if you wish - the way you are thinking of doing it sounds good. Another method of introducing solids is called Baby Led Solids and this means that you give the baby finger food and let them decide what and how much they want to eat. One advantage of this method (as well as saving time with pureeing), is that children are exposed to different textures and tastes earlier and generally become more adventurous eaters and able to eat family food sooner (which makes life much easier!). If you are interested in this approach, there is a thread on Baby Led Solids you can have a read of.

GL hun. Don't worry too much about when to increase the amount. Just look for signs and see how you go. The main things is to make sure the milk intake doesn't reduce.