I will probably get a slap on the wrists again for giving advice, but here We go. If I can give advice that will work for you then I will give it.
LOOOOONG Reply
Start off with your appliances (Everything). Check all the labels and get a total amount of Watts needed. Add 2500W for your geyser and another 2500W for your stove. This will give you a figure around the 30k's of Watts used. Now work out times. When do you need your geyser, when do you need your stove, when do you need Sound or TV etc. Place all of them in a timeline. E.g. I shower in the mornings my wife bath at night, and the maid wash dished at around 11am. So, Geyser is needed 3 times a day. Stove gets used once a day and that is for cooking between 6pm to 8pm. Rest of the time not needed. Now you work out peak wattage per hour of day. (You will see why a bit later).
So, lets say you ended up with a total of 30k Watts as maximum. You now add that into your hourly sheet. and bring it to percentage. How much of 30k Watts do you need to run your geyser for X number of hours 3 times a day. Same with everything that uses electricity.
So, far sound confusing but if you go through the list you will note, the geyser will not be working the same time as your stove, so you cut out 2500W because they use the same amount. TV works but radio do not etc. So, you find duplicates that will run at separate times (But seldom together. Each time you deduct 1 of your total wattage needed. If you do it right, you will end up with anything between 1700Watts to 8000Watts. Now you have a maximum household wattage figure. The hard part comes now. What do you need when there is a power cut or failure. Do you need a washing machine?....no, can do washing when there is power again. Do you need an Iron, nope can wait for power. So you take of all non-essentials. My essentials list consists of TV's, phone chargers, studio, office, routers, lights and stove (As explained it is 2500W for either stove or geyser). That is for my household so yours might look different. Without lights I cannot see, without my studio or office I cannot work, without phones we cannot communicate and without TV I have the wife bugging me. So, anything can be off as long as the TV is working (LMAO)
Now once you deduct those you will get a minimum figure. Usually around 1000 or 2000Watts. Lets say you came to 1749 Watts. Now you need head room. Incase someone switched o the radio while the tv was on. This is calculated (W*3)/2. So 1749 Watts I will need 2632.5 Watts. My minimum invertor I can use is a 3000 Watts invertor.
Now that you have your minimum invertor size you start shopping. There are awesome systems with 52V lithium batteries etc. Keep in mind the fancier you go the pricier it gets. This is where I love the Phoenix range. Start small do not rush and make it an investment and not a "Got to be done now" thing. I did mine the following way and then you will understand why.
First I needed light. I do not have 100% vision (Never had it) and doubt I will get it. I need to see where I am going, and my wife needs to see where she is going. SO, getting "important" light up during power cuts is important. I do not need my bed lamp to work but Mahn if I can have the celling light on to see where my pajamas are then please switch it on. Bathroom light is minimal, corridor a MAJOR YES and so we go on. Let's say 7 Lightbulbs totaling 50 Watts. So, Phoenix is a separate unit system. I needed 100W to see. Just to see (Nothing extra). The less voltage you put in the more it sucks your batteries dry (Remember that when buying invertors). I ended up buying 2 12v Solar Gel Batteries, a normal Gel battery charger and a Phoenix Blue 24/100 invertor. WHen we had "Mains" the batteries charged and when it failed I was able to swich over and have lights. Had wires running into my DBboard to the lights side to have it working without changing all sorts of things everytime.
Lights done, I went bigger. Took the lounge and decided I want the TV and radio to work during no power. Bought a 24/500 with an additional 2 batteries but used the same charger. Just made it work harder., added it to the system and that part ran my wall plug in the lounge. This way I went and did it to each room. Gave it just what it needed to run during power cuts. Note, each time you calculate you take the one higher to what you need. After doing all the rooms I recalculated and found I have an extra 3000W which I am now using for my Geayse/Stove. Eventually added a phoenix charger and Solars etc but the project was done over time and not overnight. Today I have a HUGE system, 17 24v banks with shakers, 2 solar panels per bank (100W) still an invertor per room and have blue tooth to control where I need more or less power.
DO yor calculations, I am on the forum somewhere usually, when you have all the figure drop it here and we work though it. You might even get away with a 48v 2500W hybrid without solar charging.