There's a lot of moving parts involved when you replace the hot water system in your home (or design a new one). For the most part it's pretty smooth sailing. I've just highlighted a couple of nuances to consider then it comes to gas gsyer installation. For more information on geysers check out the installation section of this site.
Firstly, remember, there are two "plumbing" aspects to a gas geyser installation.
Most gas companies installing gas geysers can do both, but of course you can get your own plumber to do the plumbing and get the gas company to do the gas reticulation. Just bear in mind you run the risk of each party blame each other if things are not up to scratch.
Because gas geysers are instantaneous, where you place the geyser is significant. Two things are significantly affected by location (distance from geyser to faucet).
Waiting for the hot water to arrive drives humans insane, on gupta-style-palaces, they ever put circulating pumps into the mains so the water is permanently heated and ready to rock and roll.
We are a water scarce country, and so being mindful with water is the non-dick thing to do.
Obviously the closer the geyser can be placed to the faucet the better, but things get complicated when considering multiple points. Also some of the hoiti-toiti estates wont allow you to place the geyser on public facing walls because it's an eyesore and you neighbours don't wanna see your plumbing.
In the winter months, when the ambient temperature drops, a long run length from geyser to faucet can lead to pretty significant drops in water temperature, so there's that.
Gas geysers like their electrical counterparts can be installed indoors or out. Most of the time we like to install outdoors because then you and your geyser are not competing for the same oxygen in the room. Also, they roar while they're operating and not everyone likes the sound of napalm first thing in the morning.
There are times to install indoors though. And installing indoors does mean you can get a lot closer to the faucet and also you can see the unit and control the unit easily (some units have digital controls on the face plate). You also don't need a protective weather box with indoor installations, which can save some bucks
Bottles come in 3 sizes, 9Kg which is knee height, 19Kg which is waist height and 48Kg which is shoulder height.
Gas geysers are relatively high consumption devices, so the bigger bottle does save you from having to replace them often. But the bigger cylinders are more difficult to move around and to transport. Most reputable gas companies will deliver and connect your replacement bottles for you so this should overcome these problems.
You can use any size cylinder on a gas geyser without problems, even a little 9Kg bottle can supply the geyser without hiccups, so if there are any reasons why you can't use the larger cylinders it's no problem, you're just going to be replacing bottles more often.
The big thing with regards to bottles is that you want to have two. One bottle is connected and one bottle is on standby, so when you run dry, you can switch over and have enough time to contact you gas supplier and get you empty exchanged. The alternative is not an option. You want two bottles!
The one PIA that gas geysers suffer from is running out of gas. There is no easy way to check how much gas is left in your cylinder or to be warned when you are running low, so you are flying blind when you hop into the shower. At some point your are going to run dry, and it's probably going to happen while you are showering (because Murphy). Then you have to go outside with your freshly lathered ass, find the bottle cage reach in where the spiders be and switch the bottle over (hopefully your delivery team actually opened the bottle in prep for you).
With telemetry you can solve this problem. The telemetry system automatically switches over for you when the bottle runs dry, it then notifies us via 3g that you've swapped banks. We'll contact you and demand a ransom to deliver the replacement and you go about your business trying to take over the world. Everyone wins