Personally, I haven't tested it myself that's why I can't say anything regarding to the system impact.
Yesnoo, you should try to test it yourself. Just install and see if it is suitable for you. If you don't like it you can uninstall...
What issues do you have with applications running multiple processes?
A custom installation allows you to define what components should be installed. G-Data Total Protection set to Minimal only installs Anti-Virus. If this is the case, download/try/buy G-Data Antivirus instead of Internet Security/Total Security.
Screenshots: G-Data Total Security w/ Anti-Virus only (& Settings)
I have tried G Data in the past.
For me it's a good security program with good signatures, a very good web filter and an excellent behavioral blocker.
But i have a 7 and a half years old laptop and because of that i had experienced slow browsing.
Unfortunately i haven't tried the settings for slow computer to see how it performs.
Maybe i could have normal browsing speed, i don't know.
Overall it's a good software.
I installed G Data Internet Security 2016
Custom Install i.e installed only AV & FW.
It seems good overall i.e system boot, programs response, browsing, etc...
The installer is app 225 MB. When you install it mention "Downloading setup components". Guess it downloads the databases. And databases seems very huge as it took 15-20 Mins on my 4 MBPS connection. Databases seems app 500 MB + as per my data plan i.e I checked my data plan after completing install & app 600 MB was reduced.
Overall the component download + install took app 25-30 Mins here.
GUI, settings, options, etc... are good.
9 Processes. Not doing anything around 70 MB. Browsing with Chrome around 150 MB.
And seems PUP protection is good.
Overall seems good.
I dont like too many processes. Its personal thing.