Put your computers on a UPS, even a small one. Just protecting yourself from short power outages will save you a bunch of downtime. Even if you resolve your overload issue, this is still worth it.
Most computer users today can get by with a laptop that's under $500, giving you built-in battery backup & portability in a compact, low-power package. Plug it in to your keyboard, mouse, and monitor the same as your desktop today, so your work experience doesn't change.
The power strip you linked to (http://www.cyberpowersystems.com/products/surge-protectors/home-surge/6050S.html?selectedTabId=specifications&imageI=#tab-box) doesn't appear to have a breaker. I think that whoever wrote that was just confused about what it means to be rated for 15A.
If your coffee maker and space heater are in the same location, you could plug them into mutually exclusive switched outlets. You'll need:
A steel square box, and an appropriate face plate
A regular duplex receptacle. 15A or 20A can work
a 3-way switch
cable
plug (15A or 20A, to match the recep)
fittings
Snap off the tab on the hot side of the recep, then run short leads from those 2 screws to the 3-way switch. This will let the switch choose one socket or the other. Plug in the heater on one and the coffee maker on the other. Now it's easy to make sure only one is in use at a time.
(Later I will add some pictures and other details. If anyone has pointers to the correct fittings and cable, please comment.)
Ok. The fundamental rule is that currents must be equal in every cable or conduit.
Yes, current travels in a loop. But in actual practice, we squeeze that into a "tree" topology. Imagine you draw a tree on a piece of paper, and send an army of 2-dimensional ants (current) to explore the tree. They are not allowed to hop across branches, but they can wander from branch to branch without going back to the bottom of the trunk. At any point on the tree, if you count the total ant passages, exactly the same number of ants (current) go up any branch as come back down.
This equal flow assures the current does not induce magnetic fields and eddy-current heating into nails, sinks, piping and other metal parts of your house.
Now it's OK to have 3 wires, 10A going out on one, 2A going out on the other, and 12A returning on the third. That's still equal. That's how a sometimes-on switch wire can travel with an always-hot.
Multi-wire branch circuits
That is also how a multi-wire branch circuit works, which is what you have on 14L and 16L. It's not an accident they are 2 numbers apart; they must be on opposite poles or they will overload the neutral.
And it's perfectly fine for part of a multi-wire branch circuit to have one side branch off in another direction, as in 16L. However its neutral must run with the partner hot. So whatever is going on in 16L, you must make sure that wherever the hot runs, the neutral is right next to it.
If you're working in conduit, as I suspect you are, your local actual electrical supply house sells THHN wire in 11 colors and tape in 10. Use different colors. Gray and white are both legal for neutrals, so when you have two circuits in close proximity, ask them to sell you some gray neutral wire.
You see where there are points where the MWBC splits off to just one hot with just one neutral. That is a prerequisite for working with GFCI+receptacle devices. That is fine, again, keep the hot with the neutral at all times. Now, a few new Code requirements with MWBC:
Anywhere both sides rely on the same neutral, the neutral must be pigtailed. You must be able to remove the device without interrupting the neutral wire for either side.
Both sides of the MWBC must have a common maintenance shutoff, which in practice means thet must be on a 2-pole breaker. When dealing with duplex, you get a "quadplex" that is a 2-pole in the middle and two singles on the outside, like this one.
Best Answer
You could run the power to the dishwasher and disposal through a current sensor and contacts on the sensor in series with a coil on a relay. The power to the water heater could be taped ahead of the sensor, and connected through "normally closed" contacts on the relay. When current is detected in the sensor the contacts on the sensor would close, energizing the coil on the relay opening the N.C. contacts, breaking power to the water heater.