If i may i will quote some notable players for you and their opinions
Weresloth wrote:Clustering tends to be frowned upon, as if you get raided, all of your planets tend to get hit instead of just one or two
SpacemanSpiff wrote:I strongly agree with Weresloth. Clustering invites trouble. You might as well put out a sign for fleeters saying "Bend me over and raid me, baby". No matter what style you are playing, spreading your planets out is a good idea. It also allows playing style flexibility. You can still mine with spread out planets, and it leaves open the possibility of going fleeting in the future, whereas if you cluster your planets it limits any future fleeting.
I agree with both of them that spreading out is a good thing...but when colonizing remeber....
Wallmart wrote:long story short Spread out all galaxies accept only 300 field planets when colonizing, leave room for future growth

Do not set up planets in one area, You will be a future farm if you do

Wallmart