For the signal problem,I used to have some for sure and at first restarting phone may return a strong signal again. But soon, I found there was no need to reboot again and again. Just turn on air plane mode and turn off, your phone may re gain signal. That's quite faster than rebooting. Hope this method is useful if you still have the signal problem.
For the wifi connection problem, I have a strong feeling that it might be some internet congested traffic that causes it. I live in China and so many chinese guys use the same wifi, which lead to no traffic to my phone. Other people kinda rob it away using software. So, if possible, think about it and change a place to have a try.
Have you considered flashing Fission? For me, the bettery performance improves a lot even though it has some random reboot and forcecloses on certain apps. It may fix some of your problem. If hardware malfunction exists, considering your case, change a another phone will be better.
For the turn on/off airplane mode.. that doens't do it for me.. I can turn it on and off so many times and I still get no signal (until I reboot)
Wifi connects but no internet part... I've tried many channels and still the same, so I downloaded a wifi check app and found the wifi traffic in my area is just stupidly jammed.. so one probably that's not my phone's fault
