I have had the s1/s2 and l5/s1 posterior fusion. The s1/s2 was done 23 years ago and I am not out 5 weeks from the l5/s1.
My recommendation is to read the thread at the top of this entitled post surgery tips and that will help you tremendously.
If you have any specific questions please post, and I will take a stab at answering if I can for you. Well wishes are being sent your way for a smooth recovery.
My layman term understanding is the plif is a fusion done in the back and the pltpf is done abdominally and posterior for patients with a high degree of spinal instability such as from fractures or in revision surgery (if the initial fusion did not set up).