I have finally go round to cleaning out the computer full of dust and the fans sound quieter now and so far so good.I can't find any specifics on the motherboard identifying any options like hotswap but I suspect its very unlikely to allow hotswapping (although I have used modified bios on some HP machines to enable it).
It might be worthwhile looking at a PCIe card to give you usb 3.0 ports if you have a free slot available? given the age I would suspect its PCIe 2.0,
there's even PCIe cards that allow SATA hot swap and built in docks that might be something to consider
EDIT: using a PCIe card with multiple sata ports and then replacing any optical drive with a HDD bay/dock could give you plenty of additional hot swappable storage.
I took some pictures of the sockets.

