Connecting switches is easy. You don’t really need to know anything. The main thing you need to avoid is accidentally creating a loop. I know that sounds dumb, but you’d be amazed how often it happens.

How you connect this all up will depend on what you want to achieve. For example, if you want to supply 10 Gbe to all ports in your home, your plan may be different than if you want to supply 10 Gbe to your office, but stick to vanilla gigabit elsewhere.

Hardware wise, you haven’t listed anything that requires a managed switch. That Juniper switch has some 10 Gbe capability, but it’s a managed switch that is way more complicated than you need. Plus you’d have to buy SFP to 10GBase-T adapters. That could set you back a couple hundred dollars.

IMO, your best value is going to be something like the Netgear XS508M, 8-port, 10 Gb, unmanaged switch (currently $450 on Amazon). There is also a 5-port version, but it’s not much cheaper. Unfortunately, that means you won’t be able to provide 10 Gb to all 12 ports in your home. You’ll need one port to connect to the ATT modem/router and one to tie in your gigabit network.

In the garage, you’ll put one Netgear 10G switch connected like this:

[ATT]==[Netgear 10G]==[TP Link 1G]

You can connect your patch panel based on your needs. For example, the upstairs office will go to the Netgear 10G switch, while the other ports can go to the TP Link.

Upstairs in your office, you’ll need another Netgear 10G switch. You’ll plug all the devices in that room directly into the switch, then plug the switch into the wall to uplink to the Netgear 10G downstairs.

Since your existing cabling is Cat6, you should be able to hit 5 Gbps without much trouble. 10 Gbps requires really good terminations. In fact, terminations are going to be your primary issue across the board. Gigabit is pretty forgiving. 10 Gbps is not forgiving at all.

get another juniper unit but they will be very loud. For quiet something like unifi since they can be loud. something like the flex 10 GbE.

If you really want 10gb get a unifi aggreagtor they are very affordable, grab a few 10gb sfp modules, run cat 7 or fiber to support the speed.

I also do think this is massive overprovisioning, starting with the 5Gb plan, but I will suspend that. How do your computer room machines connect to your existing switch? If you have existing wall ports for them then you can get away with one 10Gb switch in the garage. If you only have one wall port in the computer room then you are correct in that they will need a switch. That switch’s single 10Gb uplink to the garage could become a bottleneck but I wouldn’t worry about that since your internet connection is only 5 anyway.

In my configuration with ATT Fiber, I have a Ubiquiti UDM-SE that goes to a Unifi Aggregation Pro. The the Agg Pro then has various runs, one which is a Unifi Flex XG in my office (has 4 10Gbe ports). You can technically skip the Agg Pro and just use the Flex XG in your office.