yes the 270x will be good enough still, its beyond a 1050 i believe as i know its behind a 660, but it will save you some money if you can use it.
as for the 2400g it will only hamper performance because it being an APU you cant upgrade it so you are stuck with the 2400(technically the 1400 with graphics), all you can do is up the ram and add a dedicated graphics card, an APU is only best suited if you need a cheap solution with next to no gaming involved.
mean you could get the 1400/1500x and have the same 4c8t performance of that APU with the added bonus of upgrading, but obviously how cheap the 6 cores are in comparison, you will have better longer performance with that and as for your gpu, if for whatever reason it does fail, then you will still have the budget to buy even a decent used card if you exclude the gpu from these system specs.
silverstone usually make good stuff and its not a bad price, would depend if its atx or sfx? if its atx then a 450w focus 80 gold will be better, think the 550w not much more, that silverstone be only advisable depending on your chosen setup. just a little heads up, i have a 300w silverstone sfx that included an atx bracket, i had it fitted in the coolermaster elite 110 case which is similar size to that case i suggested and it was a godsend, okay that system was low end APU, but when you havent got a separate psu chamber it makes it more spacious for cables.
