Adafruit PowerBoost 500 vs PowerBoost 1000

I am hoping there are some folks (or at least someone) that can help me understand the Adafruit PowerBoost 500 and PowerBoost 1000.

The 500 is 500mA charger, 1000 a 1000mA charger. The 1000 has smart load sharing. By what I can tell this means the load will be connected to incoming USB power, when available, on the 1000. What happens on the 500?

Connection and pin out question. 5V and ground are connections for a 5V load. Check.

Both the 500 and the 1000 have a BAT connection with is tied directly to the battery. The 500 has 3 ground pins, the 1000 only has 2. The third ground pin on the 1000 is replaced by a Vs pin. Per the description, when there is 5V coming in from the micro-B USB power plug, this pin will have approx 5V on it (less a little due to the internal resistance of the charger chip's MOSFET). When there's no USB charging, the Vs pin will be the same voltage as the Bat pin.

Do I have all of this correct?

Here is my situation. I goofed. I planned to run a 3.3V Arduino Pro Mini, a 3.3V LCD, and a reflective optical sensor from a TP4056 with the battery and output connections. Turns out the sensor is 4VDC minimum, so I will also need 5V.

Option 1: Upgrade the mini and lcd to 5V then change the power source up to 4V or more. The Li-Ion batteries appear to have a good capacity, which I will likely need. I have not found any off the shelf boards similar to the TP4056 for charging a 2x18650 series cell battery pack. Plus I want to stay with readily available wall-power chargers (such as the USB chargers that are so prolific). So changing the power source isn't a great option.

Option 2: Upgrade the mini and lcd to 5V and add a boost circuit to drive all three items. A very possible solution, but that means more load on the step up converter and more lost power.

Option 3: Leave the mini and lcd at 3.3 and only run the sensor from the boost circuit. I'm liking this the best. Now I need to either use a TP4056 LiPo charger and a step up 5V booster or find an all in one.

I think the Powerboost 1000 is what I'm looking for, but the website is more sales brochure than technical information. Before I plop down $20 plus S&H and find out it isn't what I need. My hope is that someone has experience with the unit they can relay, or suggest another option, either Option 4 for above or a different charge/boost unit they have had good experience with. The TP4056 seems to be a nice unit meant to charge a 3.7V 18650 cell (or cells in parallel)