I don't think it's remotely necessary to do your research in person.
It's fun as hell, though, and I recommend it whenever possible. However, I did it this way because I wanted to, and because, to my knowledge, no other fantasy author had; at least, not to the level that I chose to. I'll be the first to tell you that it's a stupid and counterproductive idea to write this way. It stemmed from a paralyzing fear of a normal life, and thank God; I wouldn't trade anything for the experiences I've had while doing this. Writing has led me to some interesting places that not many authors--hell, not many people--find themselves in. My books are a way for me to share those experiences, by translating them into the familiar.
This is one way to do it.
I think what's most important is experiencing anything, and transposing it into your writing. I believe that you're doing your job as an author when you tell someone something that they already knew, but saying it in a way that that they've never thought of.
My shtick is to do this through firsthand experience; readers know a lot of the stuff that happens in my books, but they might not know why it happens that way. I also bust a lot of tropes that don't stand up in real life, and I catch shit for that as often as I get claps on the back. (One more message from a katana fanboy about how my protagonists should have taken Japanese swords with them to slice through medieval armor and I'm changing my email address, I swear to God.)
You say you haven't been in a romantic relationship; holy crap, write about that. Some of us have had it up to here with romance in fantasy novels. Write about longing. Write about soul-crushing loneliness. Or, hell, write about flying solo and being completely okay with it. However you roll. Tell us about you. That's the point.
Don't try to be me; Jesus Holy Shit Christ, I do not endorse any of this. I was nearly killed several times doing my own stunts. I've had more broken bones than I can count, I'm missing part of a finger, and I was in a coma for a week at one point. That thing in the Danakil? All my toenails fell off. I have deep enough scars to show up on an airport body scanner, my low back is held together with hydrocortisone and hope, and I've sustained so many severe head blows that I nlwgayt slka oiy bngh.
You also have the advantage of expected inaccuracies resident in the tropes. 99.99% of fantasy readers don't know this stuff. You mentioned the thing about arrows passing through bodies; everyone expects that they stick out. Roll with it. Roll with what other writers have said before you, and very few people will notice. My writing appears to resonate most deeply with an idiosyncratic type of reader who comprises a vanishingly small percentage of fantasy fans. My work crosses over from there into larger audiences, but that was accidental, I assure you. I was aiming for a small crowd who, like me, know a couple of things about a couple of things, and who want accuracy, or at least want to see the effort. I was told for years that nobody would buy a realistic fantasy; I have decades' worth of rejection slips to that effect, some stating exactly that, verbatim.
Do you. Just write. Make it work. Entertain us. And God bless.
If you have questions about how things work, post them. That's why we're here. Hell, PM me if you want. I'll do what I can.