Hi ac28962,
You can get the Thermal paste from any computer store. If the thermal paste is not applied in between processor and the heat sink the heat may not be dissipated properly and which may lead to processor failure. Yes replacing a normal hard drive with an SSD drive will make the read/write access faster on the system. But changing of the memory from 4GB to 8GB depends on the applications you use. If you use general programs you may not notice the change but when you are using graphic intense programs, (Example: Playing games, video editing, photo editing) you will notice the change.