Will these satellites have to eventually be replaced with updated models when they implement the laser sat-to-sat communication?
Each satellite will be definitely replaced after some time, I think it is around 5 years max. It seems likely they will not be replacing them with the same ones but with updated designs. Whether and when it will be with laser comms is unclear, but IMHO probable.
does anyone know why they can't use the falcon heavy for these launches and launch more satellites in one go ? It says falcon 9 carries 60 satellites per launch and I'm guessing some of the limitations are due to cargo weight limits on the falcon 9 ?
A single Falcon 9 can carry 37,000lbs to low earth orbit. Falcon Heavy carries roughly twice that mass. Each starlink satellite weighs 500lbs. A single Falcon 9 can carry the weight of 70 or so satellites. However they can only fit like ~60 in the fairing which is the same one they use for Falcon Heavy. Falcon Heavy makes more sense when you need to get similar masses to farther locations (Geostationary, Moon, Mars) or denser payloads to low earth orbit.
Interesting. I assumed that they would develop a bigger fairing but I guess they did the match and figured out the optimal size based on demand for payload size/weight