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I would like to purchase a Gigabit ethernet switch (8 port) to upgrade my home network, can anyone recommend a good brand please?

I've always found the metal casing Netgear equipment to be quite nice and also very robust. I've no experience with their cheaper home range which is plastic.

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Is it possible to get features such as SPI firewall in a switch or do I need a router?

You'd need a router. If you've got the space then find an old PC and install IPCop

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Is a hardware firewall even worth it if all the computers on the network are running software firewalls?

Yes