Yes it is possible to do other quests outside the current guide, be aware that blizzard has a limit, and this is 25. This can also be overwhelming even for the most experienced players.
Yes the quests can be added to the Objectives Frame, if they aren’t by default, check the Dugi Guides Settings, there should be options in there to allow quest tracking outside the guides etc. I can’t exactly remember the options. I am away from the computer. I hope this helps you, feel free to pop questions.