[GLOW]

lots of diff topics & scenarios so i'll just respond to the 2 questions you posed

adding a sub panel (lets say 60A 30 circuit panel) will mean you will make space for a breaker in your existing spot to add a 60A breaker in it. You will re-route the wiring for the breaker(s) that you took out of your original panel to the new sub-panel. the sub-panel will have space for new breakers that you desire (minus the ones you brought over to make room for the 60A breaker). your overall load doesn't get to be increased, you'll just have more breaker space.

if all you're doing is replacing an existing panel for one with more space (more breaker slots) and nothing more, then i suggest budgeting $1500-$2k, plus the cost of Hydro disconnecting and reconnecting power. If the electrician can plan the work so hydro just comes out 1 time it'll save you paying hydro to show up twice. if the electrician asks for more than what i said ask them to break out labour/material costs for you

keep in mind locating a sub-panel in another location further away from your existing panel (for whatever reason) will also add additional costs.