I think the key thing is to recall-- what precisely is a Gnome? Or rather the essence of one.
Half-Dwarf and Half-Halfling? No. Even by appearance, not at all. Gnomes tend to be smaller than either.
The key to the Gnome, whatever is called a Gnome, is intellect. Sure, there are versions that cast illusion and enchantment spells like breathing. And that is certainly a path one can go down.
And then you have forest (or garden!) dwelling ones who are friends with small animals, who know all the special herbs and medicines and can heal someone.
But then you also have modernized ones who excel at the latest steampunk technology....
The Dwarf is about resilience and toughness, both physical and mental who will not shrink or back down from any challenge.
The Halfling is about being quick, crafty, lucky and tougher than they look.
The Gnome concept doesn't overlap with these nearly at all-- although one might want to give them some Dwarf-like abilities due to being cousins or give them Halfling like abilities for being small, I think these were decidedly missteps in the development. It is important that they be a unique race.
So what do you need to have if you are a Gnome?
Well, use Elf as your primary template is a good beginning I think. Use that race's saving throws and attack and spell advancement.
Their hit dice would be D6s.
Weapons would be restricted like a Halfling's due to small size. I wouldn't grant them the +1 bonus to AC though. Figure it is best to leave that as a Halfling thing (since Halflings get so very little as it is).
Their spell list would be restricted to only illusion and enchantment spells.
They have the ability to communicate with (but not necessarily hold intellectual conversations with) small animals.
They would have the ability to hide, particularly in the wilderness-- much like the Halfling ability.
They should have the Tinker ability of the specialist. Although demi-human abilities all seem to be set at a particular level and never changing (mostly because the designers copied D&D line for line I imagine), I would think moving away from this model and starting low and improving would be better. So either their tinkering is always 4/6 or it starts at 1/6 and improved by 1 point every 2 levels.
I don't know what the experience points needed per a level should be set at. It would be lower than Elf. Maybe 75-80% of the experience needed to level as an Elf due to having a greater restriction on spells and weapons.