Fellowships are always harder from a community program, but you can definitely still do it in rheum. Bear in mind that rates of non-matching are going up pretty quickly and were actually one of the highest (though for various reasons that doesn't mean it's the most competitive). It's currently a mid-competitive specialty, where you could get in without research from a community program but won't have your pick of cities and should apply broadly. A&I is tough because there are so few spots. It was crazy competitive a little while ago and I think it's still moreso than rheum, but I think they're tracking more closely now.
Scores are treated pretty similarly to residency - you generally need to be above a threshold to be considered (what that is depends on the program), higher is better, and it's not the only thing that matters. Try do do well on your Step 3's but they'll probably look most closely at Step 2, which you've already done, so there's no reason to stress about it. It's in the past, so plan accordingly.
It may be good to do an outside elective to get a rec or to show them you're a good candidate - if you're hoping for the latter, I'd recommend going to a program that you could reasonably match at. Don't do an elective at Hopkins hoping to match there - it's probably not going to happen. If you can impress them and get a letter that's great, but if you don't have research and are coming from a community program you could spend that time more wisely at a mid tier rheum program that would actually consider your application. Don't forget about your home program even if it doesn't have a rheum fellowship - do some rotations there and be sure to impress the rheumatologists you work with. Be likeable, nice, and let them know your intentions.
Research is definitely a plus and is essentially required for the top ten or twenty programs, but you can still get in to rheum without it. Try to at least get a case report or something along those lines so you can say you tried. Research outside of rheum is also valuable and most of my research was actually in other areas.
I personally don't think anyone cares about conference attendance - it just doesn't say very much about you. Doesn't mean you shouldn't go - it's good to see what the specialty is like, learn some stuff about practice, network - but don't expect it to matter a whole lot. It's definitely good to present a poster at ACR if you can, but that's not "conference attendance" that's "research."
Recommendations are very important. There was a rash of, "I went to a good program, did research, had great scores, didn't match" posts after this year and I think that was because it was more competitive + the person may have had a poison pill LOR. Both rheum and A/I are small programs that will be interviewing a few dozen apps, so you can expect them to read all your recs.
Something you didn't mention that could be impactful is a chief year. It gives you more time to do research, another year to squeeze in an elective and get some good stories for your PS, and it demonstrates that A. Someone in your program actually believes you have leadership qualities / can be trusted / are in the top few percent of your residency class (which is better than them making some generic platitude in your recs) and B. You actually care about teaching and leadership (as opposed to just saying, "I love teaching and I'm a natural leader - trust me I swear it's true!" in your PS).
One final thought - just be a good resident. It's easy to think that your application is made up of all these components and you should just gunner your way to having each be strong. At the end of the day, though, you'll need a letter from your PD, letters from docs that you saw on the wards, people to funnel you research projects, other residents to talk you up to whatever connections wherever they may have them, someone to give you a shot at being a chief, etc. Be a good doctor and support your fellow residents - that kind of stuff really does have an intangible effect in my opinion.
