How important is the number of cores and threads in application development?

Question

CMS

Hello, I would like to know more about the topic of the question, which will be described below.
At the moment I have a system with an i7 6700 processor, 16 GB RAM, 128 SSD (although this is not the best Kingston UV300). Recently I thought about building a new PC to replace the existing one. The question is: how important is the number of cores and threads (very important about threads) when developing applications in mainstream languages ​​like Java, C#, C++, Python? As far as I can tell, you can do this on an old dual-core pentium or AMD, but then when you test the written application, all this turns into a rather unpleasant process (you have to wait a very long time, it’s better not to talk about running several programs). On the other hand, will there be a clear downgrade and performance hit if I upgrade to, say, an i5 7500 (in favor of a better SSD, motherboard, and PSU)? As far as an IDE like VS, Eclipse,
As you can see from my question, I'm still new to this stuff, so no giant projects over 1-3k lines are planned in the near future. In general, I would be glad if, in addition to answering the above questions, I could be advised on the relevant literature in order to delve deeper into this topic. Thanks in advance!

Answer 1

There is no CMS.
There is self-writing.

Answer 2

i7 should never be abandoned and downgraded. it now seems that the power is redundant. but it’s better to leave this excellent stone and forget about replacing it for a long 10 years (approximately as long it should last without problems so that discomfort is not felt). but everything else can be upgraded - in a couple of years, plug in another 8GB or 16GB of memory, buy a fatter ssd (you can save up by this time, I think), go broke on a video card to take a break from the code and stuff like that. But exchanging i7 for i5 is blasphemy!