I have 2 temp control mods, and only vape in temp control
And ill add that i vape stainless steel wire - a single coil 7/8 wraps on 3mm for about 0.6, and thats the viewpoint the following comes from.
Smok TreeBox - i set the watts at 40w (it goes to 75w, but on the off chance theres an issue and it jumps out of temp control, i do not want a 75w hit, i likes a cool vape do i

) the day i got it and havent touched it since, since the watts set is just the ceiling, the mod will only use enough watts to get to the set temp, and then dynamically use only enough watts to keep the set temp. Normally at the temps i vape im only using about 26w...probably less than that actually, i turned down my temp due to summer coming back the last few days and have dropped from my usual 210c to 195c
A lot of temp control use the same method, set the watts at 30 or above (i know this is what the VTC Mini makers tell you for that), then switch to temp control mode and set the temp.
But check your manual as your mileage on how it works may vary. The only time you may want to set a higher wattage is if youre using as device like the DNA200 and want a high preheat value, i.e. more watts initially to get the wire up to temp quicker (though i personally dont understand why you would want to as this is kind of the complete opposite of what youre trying to achieve with temp control in the first place)
SX Mini M Class - Doesnt use watts at all, uses joules, still dont understand it

But i set the temp the same as the TB and then set the joules to give me approximately the same vape
A number of mods may also have a heating profile setting that isnt like the DNA, where you can have soft/normal/hard (or in the case of the SX Mini (Standard/Powerful/Powerful+/Eco)) presets that change the ramp up time without exceeding the joules setting (as i understand it)
To answer directly:
Not usually, usually the wattage is treated as a ceiling and the mod will only use what it needs watts wise to get to the set temp, but exceptions may exist, check your manual or search the devices user thread on here
No. Not unless youre using one of the exceptions, like the DNA200, and set the preheat to use above the watts norrmally and actually needed to get the set temp.
Yup, it does reduce ramp up time, as do the profile settings on some mods like mine - though ive never used anything but standard, im not exactly on a time crush when i vape, its not like i have 10 seconds to get a vape in before inputting codes to disarm a nuclear warhead, in other words, i dont see the point of preheating ramp up. I really dont understand going literally beyond the temp youve set and then dropping back down to it, its irrational to me. No ones in that much of a hurry. I also think a lot of people if they werent using flavoured juices (i vape unflavoured) wouldnt do half the crazy high watts in pure watts mode or in temp control, the preheat stuff they do, i can taste the difference in single degree steps, because im not masking my juice with flavouring, and i know right where the limit is quite clearly because if i go beyond it by a degree or two it starts to taste like skunk.
The preheat of course is going to reduce battery life a small amount, but unless youre on an exception like the DNA with preheats above the normal watts to get to the set temp, its going to be safe as vaping with batteries can be.
Glad you asked about the battery safety angle. You always want to have the correct batteries that give you the best constant current drain rating possible. You'll want to consult the devices specs to know the specified current draw is on the device. But even then please check on here before purchasing batteries, as manufacturers will, sadly, often say their devices can do things like 200w with just 2 batteries (because some people get focused on the "more watts" game), but in reality its not safe and that 2 battery 200w mod should only be sold to work at a safe 133w Max. Its mostly a limitation of batteries, you'll see a lot making claims of CDR's of 35 or 40 Amps, yet most of these have been found to be bogus by a great member named Mooch here, so reliable safe high CDR batteries to run devices like the 2 battery 200w mods arent actually either a) real or b) easily accessible, or shouldnt be attempted even if they did. Most of this warning is in general and especially for people looking to use pure watts mode. Yes you are far safer if you plan to use temp control, but if you ever plan to try the ridiculous watts stuff, you need to be aware, and be as safe as you can. Sadly some mod makers will just tag every mod with 200w, even with just two batteries (and when they know you cant get the mythical batteries) when they shouldnt.
In in doubt, spend time doing searches here before buying both the mod and the battery, especially if you plan on going between temp control and pure watts
Get it right and temp control can be the best and most consistent vape you can get. Once i got a good temp control mod i never looked back and do not miss the days of endlessly rewicking and rebuilding and fiddling with watts to get a good vape. I value being able to get the same vape every time i hit the button, and for me at least , thats what i get now. I pick the device up in the morning, hit the button it works, and apart form weather variations or travel to places well above sea level (which i do weekly), i hardly have to adjust anything.