Hello
Yes, you can inter-connect both switches using a normal Ethernet twisted pair copper cable using any of the normal RJ45 ports. Of course you should consider the maximum distance of 100 meters supported by twisted pair cables. Both switches support Auto MDI/MDIX which means it doesnt matter if you are using crossover or straight-through cable. Both will work.
There is no requirement to use only SFP ports for switch to switch connections. SFP transceivers allow the use of fiber optic cable which can cover longer distances and higher bandwidth (if supported)
I am assuming that no VLANs are used and all the devices are in the same IP subnet. In that case no configuration is necessary on 1820.
Please do not connect more than 1 cables between the 2 switches because you will create a loop. If you need redundancy you should enable STP on 1820 bevor connecting the second cable. And first you should check if it will be working. Usually the unmanaged switch should forward the STP BPDUs like normal broadcast but some unmanaged switches may drop them.
Let us know if there is something else you are concerned about!