1. Nope not harmful. In fact it brightens things up for the chameleon to see better - see daylight section here:
https://chameleonacademy.com/chameleon-cage-set-up-replicating-the-sun/
2. You can get a spotlight or a linear version. You can find lots of threads using the search function if you want to research options and setups, and figure out the pros and cons for you from there (space and cost are the big ones). I got this knockoff version of a Sansi when it was on sale and it's doing wonders for my plants:
https://www.amazon.com/dp/B07C7L31K8/ref=cm_sw_r_cp_apa_i_ow-nFb6SGTKXF
For linear, you can get an Arcadia jungle dawn:
https://www.joshsfrogs.com/arcadia-jungle-dawn-12-15-watt.html
There's definitely some science behind plant lights which I haven't been able to wrap my head around yet. But if you're interested in that I'm sure you could go down a deep forum or Google research hole.

3. You can have both your UVB and a plant light running at the same time.
4. This will depend on which light type you get, what room and materials you have where you have your enclosure. My spotlight is just on top of my enclosure on the screen. It doesn't get hot. It's in a dome fixture that's on the same timer as the UVB. 12 hours on, 12 off. You might have to troubleshoot with your plants since the ones right under it will be getting lots of direct light.