Advise on primary key for detail tables (OS: Raspberry Pi)

Hello,

I have a project which will be mainly built on Raspberry Pi and some parts
on Windows.

I must have a PostgreSQL 9.4.10 running on Raspberry Pi and another
PostgreSQL running on Windows. Though, there is still a possibility that
Windows database server will be something else that is not known to me, yet.
Since Raspberry Pi is running on a SD Card, data saved on Raspberry Pi will
be copied over to Windows database system for a proper backup & disaster
recovery.

I need to keep database server overhead as low as possible on Raspberry Pi
system. That is because software that will be a running is going to do some
time essential sensor communication.

I am about to start table designs on Raspberry Pi. There is one
master-detail-detail-detail structure I should implement. Master having
serial, uuid and some varchar fields. Uuid field being primary key. Details
have serial, uuid and some smallint fields.

I recall that it is "generally" advised to have a primary key on any table
used on a database server.

My question is: Is reading performance will be faster, if I remove primary
key on serial fields of detail tables and use a regular index put on master
table link fields only? In another words, is it advisable *not* to have a
primary key on PostgreSQL table?

If answer changes according to OS underlying, I appreciate replies indicates
so.

Thanks & regards,
Ertan Küçükoğlu