Adding another router for your computer won’t evenly split the bandwidth

router is unlikely the primary issue affecting your download speeds.

point-to-point wireless bridge is better for a 450ft distance between your house and barn.

Yes , it would be solved by adding another mesh router and increasing of Wi-Fi coverage throughout your townhouse.

implementing VLANs to segregate networks within ER605 router for enhanced security and control.

i would sugged managed switch better for you it gives full control & flexibility

for outside of house it be good but y he need inside of living room ?/