very lucky man to have 3 x 1Gbps fibre. Contact your ISP and see if they allow you to remove the modem and just use the Mikrotik. and if yes, what SFP module they would recommend (muti-mode, or single mode). So the fibre feed can go straight into the Mikrotik. It's likely you can do this as you already know the PPPoE details.
as for product selection, you can layout your requirements first,
SFP cage / Ethernet port
Gbps LAN ports
what the router will have to do apart from the basic PPPoE clients and Loadbalancing (QoS ? VPN? IPSec ? L7 filter etc.)
I'd think a MT4011 or a basic Cloud Core will do. but use your requirement to narrow down to few routers and check the test page on each product.
for example, the Cloud Core Router 1009 gives you
Ethernet test results
CCR1009-7G-1C-PC Tile 9 core all port test with combo-port
Mode Configuration 1518 byte 512 byte 64 byte
kpps Mbps kpps Mbps kpps Mbps
Bridging none (fast path) 652.8 7,927.6 1,931.2 7,910.2 14,874.0 7,615.5
Bridging 25 bridge filter rules 649.6 7,888.7 1,183.8 4,848.8 1,184.0 606.2
Routing none (fast path) 652.8 7,927.6 1,931.2 7,910.2 14,581.0 7,465.5
Routing 25 simple queues 652.8 7,927.6 1,686.0 7,175.6 1,699.6 1,142.1
Routing 25 ip filter rules 615.8 7,478.3 660.9 2,812.8 668.3 449.1
https://mikrotik.com/product/CCR1009-7G ... estresults
It has a combo port (combining ethernet and fibre) so this allows you to attempt to use both type as uplink.