In addition to cutting the side missions they'd also have to address one of the bigger plot holes of the series. As a Spectre with Asari commando minions, Saren didn't need the Conduit to get to the Presidium. He and his Asari already had full access to the Presidum.
Neither of them is allowed to bring a huge amount of their own armed forces in there without reason.
You also kill Benezias entire commando unit (except Shiala) while on Noveria, their number is insufficent.
Thats why it was needed to bring a sufficent amount of geth forces
Where a film adaptation of the series would run into greater problems would be with Mass Effect 2 and Mass Effect 3. The format of ME2 would not work on film, where you introduce an entirely new cast of characters, only to have them shoved to background again in ME3.
Mass Effect 2 was the introduction for the dark energy plot (building a human reaper was one possible ending for that), while it was (especially gameplay-wise) a great game on its own, its main plot remains a dead end.
As for the Squaddies: Bioware even said that ME2 had too many of them.
While some say that you can skip ME2 (and all its DLC) entirely without missing anything important, i whould not go that far, the important things in ME2 are:
- Introduction of SR-2 (including EDI)
- Proper Cerberus Introduction (and maybe Overlord)
- Mordin
- Wrex/Wreav
- Any other Krogan-/Tuchanka-stuff that is relevant for the "Curing the Genophage"-plot
- Tali
- Legion (and the whole explanation of geth and heretics)
- Arrival DLC