Hi everyone, thanks for all your replies!
Next time I'm definitely going to a proper butcher's to get the right cut of ribs (still have to experiment with whether spare or baby back are best, as I've seen spare ribs with barely any fat/meat and these are supposed to be fattier!). I think, in my experience, that the ribs should have some meat and fat on top of the bones so they don't wither and dry out in the long and slow smoking process.
I realised my ribs were too big on the rib rack, so the ends were directly over the charcoal! Lesson learnt (first time using the rib rack, didn't have it 3 years ago) - next time I will trim my ribs down.
I think I'll experiment with both bottom and top vents, the main problem I had was I couldn't see the temperature without opening the lid to look at the oven thermometer, as my lid doesn't have a temperature gauge. I'll be buying the Maverick ET732 in a few weeks, as I've heard good things about it and that it's quite accurate, so with that I shouldn't have to open the lid when messing around with the vents, thus I'll be able to control my temperature much better (right now, every time I open the lid and adjust the vents, I have to close the lid and wait for the temperature to stablise again with the new vent positions, which means I have to open the lid quickly to check the temperature again!). Talk about doing things the hard way!
Regarding the minion method, I think next time I'll try to stack them tighter together rather than spreading out. I think I was already hitting the food grate with some of the lumpwood but it wasn't packed tight. I'll try stacking them tight and also bury wood chunks inside the pile. The only thing with these lumpwood is that obviously they are all different sizes - I bought a 5kg bag and it had mostly small pieces! I felt ripped-off, there were more small pieces and only a handful of big pieces. Perhaps briquettes provide a more even spread and better for stacking because of perfect shape/size of each one? What do you guys reckon, lumpwood vs briquettes?