It looks like someone set out to build a Rube Goldberg network, then said, "the heck with it", and bridged the whole thing without bothering to clean up the mess. https://www.rubegoldberg.com
I'd dump the bath water and not worry about if the baby is still in the tub. What a mess.
You're fastest fix is likely to connect Main Router ether1, or sfp1 to Main switch any port, Main switch fiber port to second switch fiber port, second switch fiber port to third switch fiber port, and turn off the second and third routers. You can likely default the configuration of all three switches without danger (especially on your test network). Give them management IP addresses starting from 192.168.x.10 - 192.168.x.12. Make sure they are configured to be pure switches.
Your main (and only router) will be 192.168.x.1. If you want to VRRP the spare routers for redundancy at the main location, you can put them in 192.168.x.3 and 192.168.x.4. But I'd probably just configure them as cold spares with duplicates of the configuration of the primary router so that if something goes wrong, whoever is on-site can unplug one and plug in the next spare. I don't imagine 20 minutes of downtime is going to cause significant issues for your setup. Once you understand what you're doing you can complicate things and add-in automatic failover.
You are probably better off to default the config of the main router, use quickset to get the IP range you want on it. Then add in port forwards under IP Firewall NAT. Possibly the server inside will end up with a different IP, so you may need to change the rules to take that into account. You may want to make the main LAN subnet match the existing server IP addresses, if they are all in the same subnet, just to avoid having to change static IPs on the servers.
Add the no-ip script if you're using it. Easier would be to enable the IP cloud functionality. At that point, everyone should be able to get Internet.
Make sure your admin user password is REALLY good. Do the same for any other system users. The no-ip password did not qualify as good, maybe decent.
I would add a rule to the input chain, just before the drop rule, to allow your remote IP address(es) to manage the router from offsite. If you have multiple addresses from which you may want to manage the router, you can put them all in an ip firewall address-list and use src-address-list in your input chain allow rule.
I would enable L2TP/IPsec VPN so you can directly attach to everything up there from offsite. Just checking the box in quickset and adding a REALLY good password, different from your MikroTik admin password, will probably be sufficient to configure the router. It's easy, so just do it. It will save your bacon some day.
I will guess that this is all probably about 30 - 90 minutes worth of config time for a newbie. :-) It's even less config time if you just let it use 192.168.88.1/24 on the internal LAN.