I suggest you get the book, "Saving your Sex Life, A Guide for Men With Prostate Cancer", by Dr. John Mulhall, it will answer many of your questions, and it will explain "Penile Rehab" programs that you may want to focus on. Also, you can find many of Dr. Mulhall's videos on You Tube ... they go over much of what is in his book.
Your still a bit early to expect much in the way of erections, but it is good that you've started on lose dose PDE5 inhibitors ... a good start to a Penile Rehab program. If, after a time, you do not have a response to the pills, you may want to consider injections (Edex, Caverject, Trimix, Bixmix, etc.), as part of your Penile Rehab program. As I understand it, injections work for about 90% of the guys who need them. Injections do take some getting use to and you should only use them under a doctors supervision. Talk to your urologist, it sounds like you are already headed in the right direction.