Regarding the memory, that's going to be a bit of a pickle. Here's why, and I do understand that hardware availability and pricing is legitimately crappy there in a lot of cases. Especially if you have to pay shipping to bring it in to the country. Still, that doesn't change the facts below.
Anytime you plan to use more than one module, for dual, triple or quad channel operation, is is ALWAYS a good idea to buy them in a matched, tested set that is already known to work together. Even buying IDENTICAL part numbers is no guarantee that any two modules will work together because there are so many variables involved. Usually there is some room for compatibility differences, but a LOT of the time, more and more as time goes on and systems become more specifically finicky to differences in hardware, there is not.
Modules with the part number XXXX this week might use different memory chips, from a different chip supplier, with different numbers of chips or not even having the same number of sides containing chips, then the same XXXX part number that came from a different batch of chips next month. That means they may or may not work together in multiple channel configurations, or at all.
In some cases, even modules that came off the exact same production run but were not tested to be compatible with each other before they were packaged up and sent out, ie, bought separately NOT in the same package together, might not be compatible. I've seen this MANY times where somebody buys two packages of the same module, rather than one package with two modules in it, and they would not work together although each module worked fine individually. It is NOT uncommon. It is also NOT in every case.
Sometimes you can slap two totally different modules in together that are not even the same speed, voltage or latency and they will simply work. Often though this is not the case. It is ALWAYS a crap shoot unless you buy them together and even THEN sometimes it still happens, but a LOT less frequently than when bought separately. For examples of this you can check out this thread here where I provide specific examples of how modules that are even the same model and part number, are hugely different.
So, knowing that, if you plan to add another 8GB, or another 16GB, I'd do it with a pair of sticks so that if it does work, you get dual channel operation from both sets. The problem with that is, two sticks is two additional chances that one of the four sticks doesn't want to play nice with the rest of the sticks. If you're willing to take that chance, then I'd go with a matched set of sticks that add up to whatever capacity you want to shoot for. Or, sell what you have and get one quad set of 4 x8GB.
Honestly, you may not see any benefit from adding memory at all so I'd first determine if you are even USING anywhere near the current amount of installed memory when you are in the middle of a large project by downloading and installing HWinfo, run it, choose the "sensors only" option and disable the "summary" option. Check the first few lines to see how much of the installed memory is actually being used during a big project. If you're not using more than 12GB total, then adding more memory is probably pointless.
Power supply is an even bigger pickle where you are because I know for a fact that good models are hard to come by there and are expensive, when you CAN get them.
This thread gives you my recommendations regarding power supply models, but the capacity will depend on what graphics card you end up going with. For most systems a good 650w unit is more than enough. 750w is recommended with a high end system if you plan to overclock the CPU or graphics card, or both, in most cases.
These recommendations for capacity are pretty much realistic and I tend to use them. They allow for a bit of headroom but that is ok. Good in fact.
http://www.realhardtechx.com/index_archivos/Page362.htm
My model recommendations can be found here:
Below you will find MY standard list of recommended power supplies and beyond that this thread is intended as a landing place for questions or discussions regarding specific units, platforms or related PSU tech, all of which are all welcome to be discussed here. If it's related to power supplies...
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