I just want to sum up my knowledge and for somebody to confirm/deny it.
Battery
XsYp - X̶ ̶a̶m̶o̶u̶n̶t̶ ̶o̶f̶ ̶c̶e̶l̶l̶s̶ ̶p̶e̶r̶ ̶p̶a̶c̶k̶ ̶Y̶ ̶p̶a̶c̶k̶s̶ ̶i̶n̶ ̶p̶a̶r̶r̶a̶r̶e̶l̶.̶ ̶e̶.̶g̶.̶ ̶1̶0̶s̶3̶p̶ ̶1̶0̶ ̶c̶e̶l̶l̶s̶ ̶i̶n̶ ̶p̶a̶c̶k̶,̶ ̶3̶ ̶p̶a̶c̶k̶s̶,̶ ̶3̶0̶ ̶t̶o̶t̶a̶l̶ ̶c̶e̶l̶l̶s̶.̶
X amount of cells in series (that’s what the “s” stands for), Y amount of cells in parallel so 10s3p is 30 cells, 10 in series, 3 in parallel
BMS
Keeps the level of multiple batteries the same.
Is n̶o̶t̶ involved in battery charging
Is not ok to use multiple ones, e.g. 2x6s bms for 12s battery
Specific smart bms can use higher one on smaller battery, e.g. 10s bms on 6s battery
Charger
Y̶o̶u̶ ̶n̶e̶e̶d̶ ̶b̶a̶l̶a̶n̶c̶e̶ ̶c̶h̶a̶r̶g̶e̶r̶ ̶f̶o̶r̶ ̶m̶u̶l̶t̶i̶p̶l̶e̶ ̶l̶i̶p̶o̶s̶ ̶i̶n̶ ̶s̶e̶r̶i̶e̶s̶,̶ ̶c̶h̶a̶r̶g̶i̶n̶g̶ ̶t̶h̶e̶m̶ ̶a̶l̶l̶ ̶a̶t̶ ̶o̶n̶c̶e̶.̶ ̶Y̶o̶u̶ ̶n̶e̶e̶d̶ ̶b̶a̶l̶a̶n̶c̶i̶n̶g̶ ̶w̶i̶r̶e̶s̶ ̶c̶o̶n̶n̶e̶c̶t̶e̶d̶ ̶a̶s̶ ̶w̶e̶l̶l̶.̶
You can use bms + power brick to charge lipo batteries. Or lipo alarm and balance charger.
Misc
You need antispark switch/anti spark loop key to avoid damage on connector And to avoid current rush that can destroy components.
Just to clarify more, a 10s 3p would normally be 10 packs of 3 cells in parallel, then those 10 sets are connected in series.
Something to add would be what the C rating of a pack means. The C rating is the amperage that the pack is able to deliver and you get to that answer by doing the Ah of the pack times the C rating. So a 5000mah 20c pack can deliver 100A (5*20=100).
The misc part is right, but I use my board without a switch, so plugging and unplugging every time without any problems about half a year now. A loop key/switch is very nice to have, but not really necessary in my experience.