@confuest,
As to the warning, if GUI (graphics user interface) is working. If it is then it's not a problem. If it isn't then it's not too hard to fix.
Also, I will tell you a command to delete all the now unnecessary files that were downloaded:
rm libminiupnpc8_1.6-3ubuntu2_armhf.deb && rm libssl1.0.0_1.0.1t-1+deb8u6_armhf.deb && rm libboost-all-dev_1.55.0.2_armhf.deb
NOTE: make sure you type this command correctly as parts of it delete files.
I'm glad that I could help!
RE: How to Install a Gridcoin Wallet on a Raspberry Pi