what would be the most suitable components to replace some relays?
You don't need an optocoupler to drive a relay; the relay has insulation already.
But your switching requirements are indeed high for a typical relay; we're talking about 2.6 million operations over the 10 year lifetime. There are relays which can handle this, but they're high endurance industrial devices, which will cost a lot more than an electronic solution.

There are a number of solid-state solutions.
For the 230V AC motors you can use a solid state relay (SSR), either as a module, or built with discrete components around an opto-triac + power triac.  

The DC motors can be switched with MOSFETs, again controlled by an optocoupler, or with a DC SSR.  

For the heating I presume the power is also AC. Then you can use the SSR, like for the 230V motors. If it's DC I would use MOSFETs.

(the linked to datasheets are just examples to get you started)