I'd start with 2iu. HRT dosing is ususally around .8 to 2iu ED. At this dose, you don't need to build up to it. Just start at 2iu/day. At your age, and with the combo of TRT, I think you will be happy with the results. As for how dramatic the effect is, it isn't going to be like taking steroids, but you will see fine cosmetic changes after a longer period of time. Many of these changes can't be acheived with steroids. I notice my hair gets thicker, as do my finger nails. The speed at which they grow is much faster too. My skin looks better...takes on a healthier glow. I can see these changes in a shorter time, maybe one month. I also see increased pumps early on. Over time, you will see increased fat loss and combined with test, you will see better muscle gains. 

I have seen a study to show that there isn't a difference between IM and sub q shots, but I always do my GH IM. I just feel that it evenly and consistently is delivered in this method. Plus, I find that there is less of a chance of skin irritation at the injection site