I have to be honest, this is one area where I think bigger is better, I struggled to get by with an Antex and Weller of dubious wattage, it was ok but it was always a struggle and guesswork whether the join would hold. They worked fine for all my 4mm work but the extra mass of 7mm was a struggle.
Taking advice from here I opted for the ERSA 80 and my soldering went from high school metal work classes to almost seamless perfect joints (in my eyes LOL). I know they are expensive, but of all my tools, my ERSA and my newly acquired Vallorbe files have paid for themselves thousands of times over in sheer simplicity and joy of use. I'm so comfortable with them I hardly realize I'm using them, it's as natural as writing with a pencil, rather than my previous scratching with a burnt stick.
I only use 188° solder for brass work and the choice of safety flux makes it flow really well. But I know many use 145° for everything but I find it a little brittle, especially if you have to 'tweak' something straight after it's been soldered on the wonk
Of course, soldering it straight in the first place would solve that problem, but that's next months lesson I'm led to believe
Multicore works very well, usually they match the flux to the solder so it flows really well, older reels are much better as they tend to have more lead in which makes solder flow really well, more modern eco friendly multicores are not as comfortable to use, I've got a roll of high lead content 20yr old multicore at work, which I guard tooth and nail, it's far superior to the new stuff we get.