NSFW - Sexual Advice - Being A Top For The First Time

Hello, I'm just going to be open and honest here, tagged this as NSFW, if talking bum sex might offend then click the little X on this tab up the top of your browser and have a lovely day!Simply put: I've always been a bottom, never been interested in being a top, when I'd tried before I go soft super quick and mission failure. It felt like a kind of selfish imposition on the other person in some way, performance anxiety, self-denial, needing to surrender to the needs of the other. The past few months I've fantasised about it, for one reason or another, and now I have the opportunity to do it with someone who is in the opposite situation to me (always been a train and wants to explore being a tunnel). We did some stuff tonight, just the beginnings, and something is awakening in me, like a masculine drive to fuck, make love, 'invade' (what I imagine straight men usually feel during sex) rather than what I'm used to - wanting to recieve, envelope, give pleasure to, cater for (you know, have a little buffet and lounge singer up there ready for his penis, hehe, ok 'cater' might be the wrong phrase). We're going to be meeting again and I want to be prepared.What am I hoping for here? I guess general advice as well as advice on these points.How do you grind yourself in and out without feeling silly?How do you stay hard when you have all the technical stuff to sort out? Ie. going in, finding the right spot, reentering if you pop out, doing all the work.Has anyone gone through a similar situation? I never thought I'd want to do this but it's like a rising rush of desire. How to balance that desire to just fuck his brains out with being a considerate and sensitive lover?I love the idea of doing this with my life companion first and only ever, is that a bad idea? Would I always wonder what it would be like with other people if I waited until I found him/her/it (might end up being a tree, you never know)? :D