I would buy a pre-assembled Arduino compatible relay board. I've seen them with 1, 2, 4, 8 and 16 channels. Many of them can handle 10A @ 240V loads. If the load is greater than 80% of the relay rating, I would use the relay to drive a contactor
If you're sold on using SSRs, yes, you can directly connect them to the Arduino. Your specs say the SSRs have a 7.5 mA trigger, the Arduino DOs are rated at 40 mA so directly connecting them means 5 or less per DO.
As a simple safety feature, I would separate the Arduino from the SSRs with an opto-isolator