Couple of specific speed daddy header quesions

Done lots of reading but neee some more specific answers. My current exhaust is welded front to back.

When applying rtv, how do you apply it? Pics would be very helpful as i have never used that stuff on an exhaust before
Use stock exhaust gaskets, just clean em?
Use stock header bolts? Any install into coolant areas?
If i was to use the sd flex for now and it failed later, can a new one be nicely welded on car or do i have to remove rear manifold?

New flex could be welded on the car but it would be much easier removing the rear header. When you apply rtv just take your finger and smear it on the slip joints for the crossover on the end of the pipe. You can use your stock bolts as well, no need to buy header bolts. I would buy the better clamps for the crossover though

Got the better clamps but they are not stepped clamps does that matter?

i used clamps without the step and no rtv and still had a leak on my crossover with my sd's. Then i got some stepped band clamps and some rtv and no more leaks now

I could not find stepped clamps locally.

new gaskets, rule of thumb for most things is usually getting a new gasket when u disturb one because it wont seal well again. especially the exhaust ones. you might even have to grind them off. i had to do that when i put on my catback.

For the O2 sensor I was thinking replace front one then use the old ones wires & to splice & extend harness. I am assuming the rear one will be fine?

1. will that be long enough?
2. I need the "upstream" O2?

Oh yeah, I didn't need to do any kind of modification to the firewall whatsoever...

Sounds like a case of ... Didn't read install thread.

RTV on exhaust.. not needed if you install properly.
Gaskets.. yup wipe
Yes on bolts, no they are in non water jacket areas.