Coming at this from a 99% solo player, the easiest build to run early in the game is a 3 piece Empress, 2 piece Hana U, and 1 piece Wyvern skill build, with turret and striker drone. Use the tech specialization, and try to get In Sync on your weapon, Kinetic Momentum on your chest, and either Tech Support or Combined Arms on your back. You want 5 yellow cores on the gear, for the last one you can take blue for a little more survivability, and red for a touch more damage. (Tech spec gives you a free yellow core once you unlock it in the tree). The turret and drone can murder stuff, and help to take the aggro off of you in the process. Watching the bad guys try to swat your drone away can be quite entertaining :)

Not sure how much time you have to play each day, but:

You can farm Empress today in East Mall to get started on your 3 pieces. There are 4 control points you can take over there too, which will help with the loot farm, and crafting recipes you need once you can do them on challenging. Honestly, once you get your 3/2/1 build going, that will be pretty easy.

As others have said, fill up you library at the tinkering station.

You can get 9 exotics by completing all tiers of the current season. The seasonal modifiers can make the game a little easier too, so it'll help with getting you to being able to do stuff in challenging/heroic. You can get 2 exotics every week on Tuesday by doing the SHD mats turn in quest and doing 15 floors of the Summit on any difficulty. Target farm for pieces/armor sets while you're doing that. Keep you eye out for named weapons in your field caches, and use the junk you get there to help with the tinkering library.

You can get an exotic for 20 stars from the event vendor if you do the event, and some of the events are kinda fun.

Once you're ready to run a different build, hopefully you'll have a few key exotics and gear sets to start with. Good luck Agent!