Gordon,
With regard to the tyres, you need to get matching ones for legal reasons. They don't need to be the same make, but they do need to be the same size and type.
Ideally for a caravan, a commercial tyre is better because they have extra reinforcing built in. The 175 tyre you mention is along the right lines as it has the 'C' after the size information which denotes a commercial tyre, while the 8PR indicates an heavy duty 8-ply tyre.
For a full explanation of tourer tyres, including how to check their age, cut and paste this link into your browser.
www.practicalcaravan.co.uk/features/tyre-care.html
Best Regards and enjoy your van
Nigel Donnelly
Editor
Practical Caravan