What are your goals for the season? Based on what you said it sounds like maybe level 20 and 1750 favor? For 5k favor or reaper rewards you probably want a full group this season - the champs are much tougher than live.
Based on what you said I would go pure gnome arti and specialize in the Renegade Mastermaker Tree:
https://ddowiki.com/page/Renegade_Ma...r_enhancements
This will give you alot of hp and 3 cure wounds admixture slas that can be fully meta'd for very cheap and effective healing. Fit in the metamagic to beef up these slas (maximize and quicken are first priority). Plus everything is centered around int - trapping, dps (harper tree) and spells.
In terms of dps, I would just go with a repeater and rune arm and supplement it with some spells - dipping in the harper, gnome and other trees. Repeater requires very little investment to be effective - inquisitive is more dps at higher levels but going with repeater allows you to invest more in other areas since you need to fill so many roles. The rune arm blast is really good aoe and with a high int and a small investment in DC gear your offensive spells will be effective as well. Gnome lets you boost the crit relatively cheaply with a light repeater while giving you some other goodies in the tree.
A quick warning - the champions this season are very unforgiving - if you are looking to go to 20 and get 1750 favor run level 1 and 2 quests on elite and run 3+ on normal and you will get both rewards without having to worry about the new champ types. If you are going to run hard+ I would study up on the new champs so you are prepared. For example not taking a fear removal potion could kill you against one champ type.