>>517
They basically did want to bring the New Republic into political chaos to make the First Order an undeniable threat without pissing off nerds by vaporizing Coruscant. The justification spun into the lore was that following the collapse of the Empire, the framers of the New Republic prioritized eliminating any semblance of an undue concentration of authority.
Given the continual drama between the core and rim worlds driving both the Clone Wars and the Imperial age, this is a reasonable concern. The way they tried to fix it, though, was to just shuffle the Republic's capital world every few years in order to avoid the progressive accumulation of power in any one location. This would mean that eventually every planet would have a Senate building that sort of just stays empty for decades at a time.
>>522
The only explanation thusfar is that the First Order knows they don't have the logistics or population to utilize the Galactic Empire's preferred method of overwhelming brute force, so they're putting all of their efforts into refined, technical, sophisticated, quality munitions and military. That's why Stormtroopers are raised from birth to be super commandos and even basic TIE fighters have shields and hyperdrives.
How they managed to turn a planet into a weapon that shoots energy through hyperspace though is still stretching it. The only clue we have so far is that in little places in the novels they keep referring to the source of the Dark Side. Characters speak of Palpatine wanting to derive the origin of that particular nature in the Force and suspecting it may be in Wild Space or even a result of extragalactic influence. The Catalyst novel sorta implies that Palpatine himself received the basic idea of a Death Star through meditation and left it up to competing engineers in the CIS and Republic to work out the practical means to realize it.
Maybe it'll turn out that Starkiller Base and any other impossible weapons seen in the sequel trilogy are connected to Snoke. Just speculation.