These issues should have been worked out by your kitchen designer. There are bigger concerns that just the look of everything. The range manufacturer will have a specification somewhere in your paperwork for recommended hood height as well as CFM requirements or recommendations. Local building codes may also come into play because the hood has a wood shell. Wood is combustible hence there will be a requirement for distance from the cooking surface.

Last but not least you will need to test the hood during installation to make sure when turned on it doesn't cause a backdraft in the home. A backdraft could be extremely dangerous to you and your family. If you hood is creating a backdraft, you will need to install a device that provides "Make Up Air" in the home.

Your range probably provides specs with acceptable clearances to both combustible and non-combustible surfaces. I'm sure combustible surfaces (wood is obviously combustible) is going to be at least 30" esp for a 36" range. Mine specified 30" to non-combustible and 36" to combustible.

Your hood should ideally be bigger than your cooking surface. Yours is already smaller and won't cover the front burners all that well even at 21" cutting back the depth with worsen the problem. So don't do that if you want a functional hood... which you should.

Most of the US follows the same residential code which requires make-up air for a hood with more than 400 cfm. How strictly that is enforced can vary by locality and whether it is really needed or not will depend on how old and leaky your home is and what else you have going on with other appliances/furnaces/water heaters/etc.