How many canes to keep depends on how large of a crop you want. Any canes that are not spindly can be kept. Let them go their own way on the trellis system; that is, do not bundle them tightly together with ties as they need a little space for proper foliage growth and fruit formation.

This is still a young planting; you may get more robust canes in future years.

And if this posting is related to your other recent post, your leaf problem may be transplant shock; you describe a lot of recent pruning and moving of plant material.

Thanks - useful advice.

The leaf problem emerged last year on the original plant and at the end of the season - so not transplant.

I have so many suckers that positioning for this season has mostly been about removing suckers to create space. Only two have been transplanted.

For spacing, should I expect the stems to send out laterals - or is that a second year habit?

Pretty sure lateral production is more dependent on cane tipping than plant age.

Blackberries, rather than raspberries, are typically cane-tip pruned to induce laterals. I have never noticed laterals forming on untipped raspberries.

Root diseases can take 2 or 3 years to advance to the point of crop failure and even then new growth can proceed right up to blooming before the canes look very sickly.