You must separate the network by VLANs (management, VOIP, cameras, printers, accounting, computers, and servers).
The question is whether to put another switch class D-Link DGS-1100-10/ME and the existing switches with Mikrotik to connect to it?
Will there be enough power RB750Gr3 under the above objectives?
but alas no. He 750Gr3 has nearly 2 Gigabit internal switching, those essentially can be 1 Gigabit in each network. You need to look much more powerful device , such as 1100, it already holds 7.5 Gigabit.
As another option, you buy a normal switch and they're already doing routing (L2+/L3)