Didn’t they announce they are spending 4 billion dollars or some crazy amount to make a new development building?

They are not buying other studios. Why would they? They are expanding themselves.

With the expansion comes to new hiring I’m sure.

Nintendo has said before that they don't like just buying studios wholesale, not unless they have already partnered with them for a while and are confident that all the developers and teams want to work with Nintendo. They also tend to go for smaller studios and only purchase them after a couple years of exclusive games: Retro Studios, Monolith Soft, and Next Level games. The most likely studio for Nintendo to buy next is Mercurysteam given the work they've put in on Luigi's Mansion and Metroid. Nintendo's 'Cash on Hand' assets are big enough ($16.37B) for them to buy any number of Japanese companies, but I doubt they would. They already corner the market in Japan and so 3rd parties with a focus in Japan will have to develop for them if they want to stay competitive.

However, if they were going to buy a bigger company I think Sega would be a smart move. Sonic fits right in with the classic Nintendo profile and they've been his strongest platform for sales for years now iirc. Plus it would bring in Atlus which is a studio on the rise as Persona and SMT are increasing in popularity. Yakuza would also come with the deal and aside from being a fun series, it would fill a vacant niche in Nintendo's typical line-up.

They're going to have to do something if all these other companies keep getting snapped up by Microsoft. They can't have partnerships if there are no partners. Mercurysteam would be a good purchase, but Nintendo needs to start locking down Japanese content, and fast. Sega would be an awesome acquisition, but I also think Koei Tecmo would be an excellent fit for Nintendo. They're already heavily invested in Nintendo development as it is. They've worked on quite a few mainline Nintendo titles such as Fire Emblem. Their single most successful product is Hyrule Warriors: Age of Calamity. They have a stable of RPGs through Gust. If Nintendo got its hands on Platinum as well, that would put Bayonetta and Ninja Gaiden under the House of Mario. 

Let me make myself clear: I actually don't like any of this consolidation going on. I'd like for these studios to all stay independent. But at this point, railing against consolidation is basically pissing in the wind. And besides Sony and Microsoft, we're also dealing with Chinese conglomerates with huge war chests and questionable ties to the Communist Party of China. Better Nintendo than Tencent or NetEase.

SEGA doesn't need to get bought , I'm am tired of many old school SEGA getting screwed by non true SEGA fans that want Nintendo to buy SEGA you guys never lived the pain of Mario winning 4th generation while true SEGA fans had to deal with Nintendo fans and their high horse saying SNES beat genesis and mario is gonna own sonic one day , you people are evil , I can understand you guys never had a gamegear , 32x + mega CD , master system , and Sega Saturn , , Dreamcast.

SEGA doesn't need to get bought , I'm am tired of many old school SEGA getting screwed by non true SEGA fans that want Nintendo to buy SEGA you guys never lived the pain of Mario winning 4th generation while true SEGA fans had to deal with Nintendo fans and their high horse saying SNES beat genesis and mario is gonna own sonic one day , you people are evil , I can understand you guys never had a gamegear , 32x + mega CD , master system , and Sega Saturn , , Dreamcast.

@Icaro ribeiro how old are you? I know your mostly into Nintendo stuff than Sega secondary maybe? but SEGA is first for me then Microsoft then Sony then Nintendo.