Is there some kind of rake in the operation of the server in one network with two (or more) interfaces?

Question

System administration

The situation is this:
A small desk, two servers. One does everything, the second backups it, plus a file washer.
Both HP 380 G8 servers.
Switch LevelOne old, 10/100. Ungovernable. Alas, here it is impossible to change it yet and it will not be possible for a long time.
The network itself is normal: 192.168.1.0/24
The problem is that the backup process loads the network in such a way that it becomes extremely uncomfortable to work.
Immediately I ask you not to look in the direction of "backing up at night." This option has been considered and left out.
The solution so far is this:
Servers have two LANs, one has a second one free. The second one (which does everything) has a provider plugged into the router (he doesn’t mind and, if anything, even doesn’t mind changing the firmware on the router). So, I stick the second server there and get:
Serv1ETH1 192.168.1.1
Serv1ETH2 10.1.7.8 (to wire)
Serv1ETH2v 192.168.1.10
Serv2ETH1 192.168.1.2
Serv1ETH2 192.168.1.11
users 192.168.1.50 and up to 70
Serv1ETH2v I will set the same interface on the second interface
Question actually such:
1. The silly switch will not go on strike? MACs are different for interfaces
2. Do you need any changes in DNS?
I want to ensure that traffic between servers runs without touching users

Answer 1

If backups are only from server to server, I would bring server interconnects to another subnet (yes, at least 192.168.2.0) I’ll give everything. And the forest can not be touched

Answer 2

1. Who prevents the network card in the Provo router from making 192.168.101.1 and 192.168.101.2?
2. Or buy a 5-port gigabit switch and plug servers and the old 100th switch into it. Or is it an exorbitant cost for the firm?