I want to install a sink, a toilet and a shower drain in that order before the main sewer down pipe, all in line, will that work?

Yes, you can do it. First, tell us what Code you fall under. You can also post sketch of your floor plan for us to see and to suggest how to run your sewer and vents. I am enclosing simple plan for 3 unit bath plumbed to comply with UPC. Back to you. Milo

Milos code mandates dedicated vents on every fixture that has a trap. My code allows wet vents, (see image) so instead of the three vents in Milos drawing my drawing just has one. Will this job be permitted and inspected? Regards, vTom