At this point there are not many questions to ask. You know the cell type and the treatment. The next 9 week is all about just making it through chemo. The side effects and potential complications are well documented on the internet and the literature they will give you. In reality most of the answers you could need are here on the forums.
There is not much you need to do to prepare for chemo. Just realize that you are going to be out of commission for about 10 weeks. So take care of any thing you think you will need to do before stating chemo (Vehicle oil change, move furniture, fix the leaking tap...). Each person reacts different to chemo so you don't know what you should keep on hand till after your first cycle.
As for coping. That is the hardest part for most of us. You just need to realize you are going to make it through this. I know it seems like the would is ending right now, but after a few months it will seem like it happened a lifetime ago. I suggest reading peoples old posts on the forums. There is comfort in seeing how others were in the same place you are right now, 5-10 years ago, and are still here giving advice.
As for the your Oncologist saying you need to start chemo ASAP, don't let that scare you. That is what mine said too.
Here is my story:
My testicle started to hurt on March 1st, but there was no lump. 2 Days later it still hurt and a lump had formed. I went to the doctor a few days later. I live in Canada so it takes time to get an ultrasound. I was officially diagnosed on march 21st. On March 23rd a lump formed on my neck (in a lymph node). I had my I/O on April 2nd, by then I had 3 lumps on my neck. I go to see my Oncologist for the first time on April 5th (Thursday before long weekend). By this time I had 4 lumps on my neck, the largest being the size of a golf ball. At my appointment my Oncologist did not discuses treatment options, only cell type and potential start dates for chemo. He told me I was an emergency case and would need to start chemo ASAP. I was then informed that the local cancer clinic would be closed over the long weekend so he was looking into flying me to the provincial cancer centre so I could start chemo tomorrow. After he talked to the head of the cancer agency of my province, they decided that I could start BEPx3 chemo next week but would need to start oral chemo (Etoposide) that night (to slow the growth over the next 4 days). 9 Weeks later my oncologist told me I was "all clear" and that there was a 90% chance I was cured.
I know it is a very scary time right now, but you will be over this in no time.