Digging is always the easy part. I most commonly dig ditches for other people. I figure time as a four to one ratio. I can dig a ditch in 1/4 the total time. Placing bedding sand, conduits, more sand, backfilling, often topsoil, and rake work take the other 3/4 of the time needed.
To be versatile, you need a great many machines & tools. Start up requires a 5 ton excavator, a track loader, a 1 ton dump & trailer. That is minimum for small scale projects. Then you need underground utilities locator, tamper, lasers, concrete chainsaw, & many more.
Factor the payments for all that, add insurance, upkeep, depreciation, & all the other costs of overhead, then decide if you can still show a profit.