No. There is no tweak (or too many tweaks) that will "break" your phone. Virtually impossible.
And you CAN have too many Cydia tweaks but all that does is start to slow your phone down.
You are having problems probably because you installed something that conflicted with another tweak.(which is 99% of why people have probelms with there jailbroken device. They just install things without even checking to see if it works on there iOS and phone model. Almost ALL user error. Not the jailbreak)
You CANNOT just install "anything" from cydia. Not even all tweaks are made for your iOS or phone model or even an iPhone at all.
You must check compatability with your device iOS and model for a tweak that you may want to install. There are a lot of tweaks in Cydia that will just mess up your phone because they are not made for your phone. Some are made specifically for older devices and iOS's. PAY ATTENTION, AND CHECK COMPATABILITY.
I have over 55+ tweaks install, over 100 extensions from Cydia, and my phone works flawlessly. It's because I knew to check and see that those tweaks worked with my iOS and made sure they did not conflict with any other tweaks I had. Very very simple.