With 1), I kind of interpreted that scene in the way that Amicus had moved past needing to always be top, not just because it's Lover's Day, but because he's changed his viewpoint. He's kind of gotten over feeling uncomfortable about being entered, because "Hey Marco, I love you!"
With 2), I have zero objections to being physically desired and enjoyed, especially with somebody like Amicus. I don't think there's anything wrong with Amicus being forward and wanting to get what he wants. There exists sexual attraction outside of physical appearances and seeing someone as a piece of meat -- being sexually attracted to somebody you're head-over-heels in love with (even if that guy is as homely as a mule's butt). This is a bit tangential, but I've had an experience where I was in love with a guy (or, in retrospect, it was probably more like infatuation); I wanted him more than anything. But when things didn't work out, and that infatuation passed, I had zero further desire to be with him physically. His appearance had not changed. He looked exactly the same, but I didn't have those romantic feelings for him any more. Anyway, that was just a bit of a long-winded way for me to say that I wanted that guy, but it was because of feelz, not so much seeing somebody as a toy. And in terms of pinning him, I don't really recall a point where either Amicus' or Marco's advances were inappropriate for the situation or their level of relationship... except for maybe the alcohol-fueled kiss. Making decisions while tipsy doesn't always end well.
Amicus loves Marco. He (SPOILERS TO ANYONE READING TOO MUCH INTO THIS DISCUSSION) proposed to him after researching human proposals and marriage customs and is trying to do all he can to get that fantasy of spending hundreds of years together, just as Marco is.
Pfft, look at me, defending a muscular cartoon wolf. God, I'm so invested.
Hope it gives you another perspective!