Learn me: Home battery backup system

I want to build a home battery backup system.  Key points:

• DC only, or DC with very minimal A/C.  I mainly want to be able to power my modem, router, network, TV, raspberry pi, charge stuff, etc.  All of these things already run on DC so going DC (battery) to A/C (inverter) to DC (electronics seems dumb).
• All of these items are physically located within a couple feet of one another in a cubby behind my TV.
• I would like it to be self-regulating.  In other words I don't want to have to charge it, switch it on, etc.  It should either be in-line with power delivery or auto-switching (and fast)
• I would like the ability to add a feed to it from a solar panel later.  In this scenario I would hope to actually power most of these items off of solar permanently, with the wall power only there as backup when we get many overcast days in a row.

I can't find any readily available DC power source for a TV - it looks like they have 24, 12, and 5v on the board so I might have to suck it up and use an inverter for that.

Where do I start?  I know the ultra crude solution is just a big lead acid (or several) battery with a trickle charger slapped on it, and a few DC-DC stepdown boards off ebay with cables running to each device and the inverter for the TV.  I'm hoping there is some cleaner, smarter, more efficient way of doing this.

I can't help with specifics, but have a search over on Youtube for "DIY powerwall". There's a whole bunch of people DIYing pretty serious home battery backup systems.

While you arent looking for an inverter an inverter might make the most sense, AC is better to have available then DC and my home inverter has a Standby option, means that when the generator is plugged in, it charges batteries and runs on generator power, when the generator is off it switches instantly to batteries. Im sure it could be figured out with main power vs generator

A good inverter has 90-95% efficiency. A well designed switching power supply has similar efficiency. While i agree that avoiding the DC>AC>DC conversion is worth something, don’t drive yourself too crazy with it. 

That list of items needing standby power is pretty short. How long do you need it to work?

This may sound like a dumb counter proposal to your project topic... but APC sells these very reasonably, with very limited risk of burning down the house. Sometimes an inexpensive UL listed device is worth it. 

....Now I need to go look at those DIY Powerwalls” videos. 

The  old Harbor Freight 45 W solar panel kit came with a charge controller that had 3, 6 and 12 V outputs along with a 5 V USB connection. No  24.

I don't think the kit would provide enough juice to keep the batteries charged for continous use. 

 I did create a small emergency unit for myself, but it is DC to AC. I used an old UPS that had dead batteries, remove the batteries removed the alarm buzzer, and powered it with the deep cycle from my van. Luckily most power outages take place in late fall and Winter when the RV is not in use and batteries are in the garage for storage. I use it to power all the things you listed, except the pi.  

Some day, haha, I will collect a whole bunch of dead laptop batteries, break them open take the good cells and build a battery for the unit so I don't have to mess with the lead acid.