No, you are not restricted to 6 colours. But first you need to understand the difference between 'process' colours and 'spot' (rather than 'special') colours.
Process colours refer to the colours used in 4 colour printing - cyan, magenta, yellow and black (CMYK), the various combinations of which can be used to produce a huge variety of colours. Think about how colour inkjet printers work - most have four ink colours and can use these to produce all the colours you normally see in printed publications. 'Spot' colours are special colours that some inkjet printers - and more importantly, commercial printers - can produce, NOT by using some combination of the four basic CMYK colours, but having a special ink of a particular colour (usually referred to as a Pantone colour, although there are other manufacturers).
Now how do you get more than the basic range of colours included in the PM colour palette? I have only V6.5 at home where I am now, but I am sure PM 7 is similar. Say you want orange. Click on the little arrow at the top right of the colour palette. The first choice on the flyout menu is 'New Colour'. Click on that and a dialog box opens. Give your new colour a name e.g. orange. Under 'Type' you have the choice of 'Spot' 'Process' or 'Tint'. Choosing 'Spot' means you are going to specify a separate ink to the CMYK range, usually selected from the Pantone colours. If you are having the document commercially printed, then if this selected, and it will be an additional colour to the process colour, you will pay extra for the printing.
But let's assume you are going to colour print it in-house (either on a laser or inkjet). Choose 'Process' and 'CMYK' in the dropdown lists under 'Type' and 'Model' respectively. Then click on the 'Libraries' and scroll down to e.g. 'Pantone Coated' (assuming you are using coated paper). Scroll through the colours until you find an orange shade you like, and click on it. This will change the name you have given the colour to the Pantone shade, so instead of orange, it will say e.g. Pantone 165 CVC. Click OK and you will see that the orange colour has been added to your colour palette, and can be applied to text, lines or fills in your layout. You can add as many of these new colours as you want. If printed on an in-house colour printer, the ink combinations will print an orange colour where this has been applied. Note that if you already know the CMYK combination of the new colour you want to add, you can input the values directly into the dialog box without having to specify a Pantone colour.
A 'tint' lets you create a dilute version of any colour already on your colour palette. e.g. 50% of 'red' will give you a pink.
In PM, you cannot outline and fill text characters. You can outline and fill shapes - different colours if you wish. But not text - although you can do this in Illustrator for special effects.
Hope this brief summary helps.