Dual WAN with WAN2 for Dst. Port 80,443

Hi!
I have a CRS326-24G-2S+ that I would like to use as router for a LAN-Party.
At the location we have a fiber connection with 50MBit/s. That connection is overwhelmed as soon as an unprepared visitor starts downloading a game that is not in the lancache. So I thought it would be great to use an LTE connection (with bad latency) for downloads and the fiber connection (with better latency) for gaming.
Since I don’t know of a better way to seperate downloads from gaming traffic I thought it might be smart to direct all TCP traffic with Dst. Port 80 and 443 over the LTE connection and everything else over the fiber.

First of all: Do you think this makes sense in principle? Or am I going at this all wrong?

Both (fiber and LTE) connections come with a mandatory router by the ISP where I can plugin an ethernet cable.
My plan is to use ether1 as WAN1-Interface for the fiber connection and ether2 as WAN2-Interface for the LTE connection
I have no problem configuring DHCP and the default routes.
What would be a good way to direct the traffic to either WAN1 or WAN2 ?

In terms of throughput so you have 50MB/s which roughly translates into common speak of 400Mbps throughput.
If you simply used wrong lettering then you actually only have 50Mbps throughput which is very low.

Just be aware that the CRS will top out around 250-300Mbps..

The problem with your approach is that it may require mangling and thus the lack of fastrack but we can limit that to LTE, downloading so gaming will not be affected.
What is your LTE throughput, since that will end up being a bottleneck as well…

How are these folks connecting to the CRS326. Computers already setup by ethernet, perhaps via switches?
Bring their own laptops and plug into ethernet?
Bring their own laptops connect via wifi? If so which wifi?

Nothing is clear here.

The throughput of the fiber connection is 50Mbps. The LTE connection is roughly 300Mbps. Megabits per second. Not megabytes. MBit/s is a common abreviation for that where I live. Sorry for that.

All computers will be connected to the CRS326 via ethernet cables. No more switches, no wifi.

Assuming one flat network for computers.
The concept is something like this.

/routing table
add fib name=useLTE
/ip firewall mangle
add action=accept chain=prerouting dst-address=192.168.70.0/24
add action=mark-connections chain=forward src-address=192.168.70.0/24 connection-mark=no-mark
dst-port=80,443 out-interface=LTE protocol=tcp new-connection-mark=get-programs passthrough=yes
add action=mark-routing chain=prerouting connection-mark=get-programs
new-routing-mark=useLTE passthrough=no

/ip route
(route for fibre wan if not set in ip dhcp client distance=1 routing-table=main )
(route for LTE wan if not set in ip dhcp client distance=2 routing table=main )
add dst-address=0.0.0.0/0 gateway=LTE-gateway-IP routing-table=useLTE

/ip firewall rules
(forward chain)
add action=fasttrack chain=forward connection-state=established,related connection-mark=no-mark

Thank you! That helped a lot.

Okay I just looked at what I gave you and I see an error.
I should NOT have included the out-interface because we dont know it yet LOL.
The purpose of the mangling is to make that choice 'forced". Simple to remove the additional noise, should make the mangle more useful.

Thus from
/ip firewall mangle
add action=accept chain=prerouting dst-address=192.168.70.0/24
add action=mark-connections chain=forward src-address=192.168.70.0/24 connection-mark=no-mark
dst-port=80,443 out-interface=LTE protocol=tcp new-connection-mark=get-programs passthrough=yes
add action=mark-routing chain=prerouting connection-mark=get-programs
new-routing-mark=useLTE passthrough=no

TO:
/ip firewall mangle
add action=accept chain=prerouting dst-address=192.168.70.0/24
add action=mark-connections chain=forward src-address=192.168.70.0/24 connection-mark=no-mark
dst-port=80,443 protocol=tcp new-connection-mark=get-programs passthrough=yes
add action=mark-routing chain=prerouting connection-mark=get-programs
new-routing-mark=useLTE passthrough=no