Guardians are not made for damage dealers, compared to other classes, trying to do so takes a more narrow gear set that will be an issue to put together. Mages can be rough on basic gear in groups because you will go through a lot of mana. It's easier to Melee feeder with your swords.
There's only a few ways to go about it without having specific gear for each class.
It's either Daggers, Axes, Caster route - Which would include dex robes (light armors are the best because you can use them on all the melee classes, so it's one type of armor and that's it.) Dex charms that are light or wilds if you plan on getting to headhunter) For caster you'd just need an ee damage charm set, int robes/int robes. This is the more popular way to go and because of that it can be tough to put all the gear together cause it's sought after.
Or
Swords, Axes, Caster. - Which would include Strength robes, Strength charms (lights or wilds for headhunter) Axes you can use either strength or dex so it doesn't matter if you go swords or axes. The one obstacle with this set up is Monk, You'd have to use your caster gear and cast monk. Yes you can go battle axes on headhunter but again it will be hard to put a set together.
Those are the two minimum gear set ups. That's without any Tank armors, Heal charms.
Other options for you since you have a sword set. Monk is the issue. You either have to plan to cast monk or he needs his own set of gear. Currently Monk is imbalanced, he only uses dexterity based weapons: Dagger, Staff, Spear. So you'd have to pick one of those and then get Dex armors and Charms just for monk. Going Melee on monk is much easier. It's easier to find gear to use and game play on melee monk is easier and will do more damage than the caster set up you will find for him. Staffs are cheaper and not to hard to find, Daggers of the low or average ee range can also be found. A full spear set is the hardest to find.
Most people change as they come to the class. So plan on the monk and finding the gear you want for him. Then you have it when you make it to him and Ninjas can use swords so. You'd have time to get caster gear if you don't have it in case you pass to warlock.
It is going to depend on how often you plan to play, if it will be more solo climbing or groups, and if you're looking to keep/play the game for a long time.