Thermal paste can be partly personal preference. I like OCZ Freeze or AC MX-2, others will no doubt recommend AS5.
For cleaning, use a q-tip/cotton bud and rubbing alcohol, or a product such as Arcticlean or equivalent (I use some Akasa fluid myself).
Whether your heatsink/fan will work - check the specs on the CPUs. If the TDP of the newer one is the same, it should be fine but keep an eye on temps. If the TDP is higher, I recommend you buy a new cooler.