No. Largely right, but No.
A random one-time pad is secure until/unless the decoder gets his hands on a copy (Though you might want to encrypt a prime number of bits at a time. I'm not sure what happens if you encrypt chunks of characters.)
Also, public key encryption (say twofish, or even AES) is probably safe if you have a long enough key barring either a theoretical breakthrough in factorization of decent quantum computers. But you might be wise to not use the default parameters. (What you *should* use, I don't know. I'm not a cryptographer.) But say that it's good for five years as an estimate. Note that without that "theoretical breakthrough" or quantum computers, a decent key length will be safe for the lifetime of the universe...IF decent parameters are used.
If you're using a one-time pad, you don't need to secure the message, only the pad. But you need an out-of-band secure means to transfer the pad.
OTOH, if your computer has WiFi....well, the computer probably isn't secure. If it's connected to the internet, then it probably isn't secure. Etc. Message interception in transit is only one means of interception. Interception when/while/after decoding is another. And a trojan is an excellent way to intercept the message...though it needs to be a bit more targeted than just recording everybody's messages.