To get Remmy used to you more quickly, there are a number of things you can do. If you have a shirt/top that you don't mind giving up, than wear it for a day with your usual purfumes and put it in his cage once it smells of you, than he can get more used to your scent. When you have him out of the cage, wear a big baggy jumper that he can snuggle in and run around in. Also, when you let him out, you could just sit or lay and ignore him and after a while, he will probably come to you and let him explore you.As he gets used to you, if he comes near your hand, pick him up and let him run from one hand to another and keep him moving, don't give him time to think about it, just keep him moving on your hands so that he gets used to them and realises that they/you arn't dangrous and hopefully he will eventually stop being so jumpy. Giving him treats is good to
Speak to him gently, it takes patients, but I'm sure he'll take to you pretty quickly
I think it sounds a bit like Da Vinci is showing Remmy who is the dominate one, this isn't unusual and as you say it does sound like things are going well. I think it is normal for rats to sniff eachothers boy-parts. I think it is okay that Remmy is hiding in the paper roll tube, it will be a bit unusual having another rat in his cage, so he is retreting to the tube as his safe spot. Before you try putting them in Remmy's cage, clean it out really, really well, so almost every smell of Remmy in the cage is gone and no-one feels threatened and it makes everyone slightly more relaxed. This might help.
The last thing I'm going to mention is that when they are out of the cage together, put something, like a liquid or some sort of scent (a good one is vannilla essence) on them (down eachothers back usually) so they have the same scent, this also makes things more relaxed between them
Oh, and the bigger the cage the better, Remmy will be fine and I'm sure he'll love the space he has
It sounds like your doing a good job, and I hope the information/advice helps
GoodLuck, keep us updated on their progress