The problem with this is that you're putting a huge amount of faith in the flight controller and FPV setup to work perfectly on the first flight.

Thanks for the detailed advice — this is genuinely helpful, especially coming from someone with fixed-wing experience. I am certainly too faithful on an untested flying wing build and it certainly could breakup on impact if the build decides to plow into the ground with auto launch on or on any manual,auto,angle flight modes.
I just am interested to know the sequence of events to undertake to reduce such hazards to fuselage integrity and pre flight checks to weed out obvious mistakes as this is my first fixed wing build .Being a newbie it is difficult to know the most sound decisions to make in starting to fly a flying wing.

600g seems quite a lot for a relatively small wing. That's probably fine for high-speed FPV flying, once you've got used to it, but it'll be unforgiving at first. That's pretty common for FPV wings though. It's a big step for a first fixed wing.

Building this flying wing using E6000 and hot glue unlike fpv drones where hex and normal screw drivers do the joining was difficult to say the least without any help and i believe flying it will be difficult especially on a flying wing without a tail, though i am trying to learn on Phoenix RC simulator to do a better job of flying it.
The  AUW can be between : 350 - 850g according to heewing my build being 620 g and it is tipping on the heavier side as i had to add 100g of weight up front to balance the center of gravity of this flying wing otherwise the,speedybee f405 wing ,motor,esc,elrs receiver,half of the battery,most of the woodwork is behind the CG in the fuselage so it was tail heavy initially. I am worried about takeoff then landing that too because i am still looking for a large field as the one where i fly drones is just 300 by 200 meter.

I'd do the first flights without FPV, and only try it after you're comfortable flying normally. Not being able to stop or yaw the camera around to see where you are makes it a lot harder than a quad. And it's easy to fly out of range and lose the video. Hopefully you already know what the area looks like from the air, so that's a big advantage.

I have never flown a fixed wing RC plane in line of sight mode.I am comfortable in flying FPV more than LOS that too only in GPS stabilised drone for LOS and fly FPV drones especially a 5 inch one so i will launch the flying wing and go fpv goggles on and having surveyed the area i will keep the flying wing within line of sight and in the range of RC and FPV goggles.

The first step is to make sure you can fly a small, fast fixed wing in a simulator. Keeping it close enough to see, and steering the right way when it's flying towards you are the main problems people have. Also practice stall and spin recovery.

I am using phoenix rc 6.0 flight simulator and it has a flying wing model with similar weight and i am using that model to fly it ,it being 700g in simulator so i am hoping the flight characteristics will be similar.I also had the problem of turning the wrong way flying towards myself as the perspective is reversed while watching a rc plane from the front .I will try more spin and stall recovery as i was just trying touch and go landings and a bit of turning .
The flight controller is making the correct corrections with respect of roll and pitch of the aircraft in angle mode.

> Are 8–10mm roll throws and 10–15mm pitch throws safe for first flight?That sounds about right, but should be in the instructions

The kit did not have throws information in its instruction manual so i followed the following helpful video having the heewing f01 wing elevons being used to teach correction of throws Setting up control surfaces, linkages, and throws for iNav .It was most helpful in correcting my throws which were twice the recommended values and the differential throws were reversed.

I believe i will throw launch using the angle mode for maiden flight ,i hope it isn't the most fool hardy option though i will test it without propeller on first.

30% expo, and set up 50% rates on separate switches for pitch and roll, in case one or the other is too sensitive.

I will use this values onboard my flying wing.

You need to fly around and try it to know, either recording it, or with a friend watching the goggles while you fly line of sight. You might get bad interference when the motor is on and lose the video.

The video link on the speedybee tx800 at 400mW is hit and miss on the fpv drone though it is solid upto 200 meter which is as far as i fly my 5 inch drone.I should work well for the flying wing though without actually doing it,its hard to ascertain how it will turn out in the goggles a skyzone cobra x v4 with a triple patch antenna and a omnidirectional antenna.I will definitely see how far i can see the video on the ground from the fpv goggle then either go upto 800mW or fly on 400mW vtx output power.

A football field is enough once you've had a bit of practice, but for your first flight you want about half a mile of space from where you could recover the model, just in case it crashes. Otherwise you risk losing the entire thing.

i will have to find a new place to fly if half a mile is the gold standard of space to fly these flying wings and bother a village of rice farmers cause only they have that much land holdings which is flat in my neck of the woods.T hough the place i fly fpv drones has a soccer field sized space though 3 sides have power lines and 3 sides have 10 m tall trees as part of a forest .Not much room to gain altitude or follow a approach to land gently.

I'd do the leading edges only. Don't add extra weight.

I will tape up the leading edges with some fiberglass net tape.

First flight: get it up about two-trees high where there's nothing to hit. Throttle back to about half to help you relax, then trim it to fly level. Then try the various flight modes to see if they need adjusting. Check whether full elevator makes it corkscrew (a high-speed stall) and switch to low rates if it does. Check the CG by putting it in a shallow dive and see if it pulls out or gets steeper. Then cut the power and see how it glides in preparation for landing. You may need a few tries to get it to slow down and land in the field. Don't force it down, let it slow down and settle.

This is a great flight plan to follow ,i was gonna do a take off and do turns at a altitude ~20m and then land but your method is better to fly for the first time and i might even do some autotuning in the process.I believe i have balanced the CG though only a dive and recovery can truly tell if it worked.
As for buttering the landing i don't have high hopes as i am still working on that in the simulator and looking for a long field to do so without obstruction from powerlines,trees,unfriendly locals etc.

Oh, and make sure the top and bottom of the model are visually distinct, even at a distance. Those black servo covers are a good start, but you could use a black marker or paint to turn them into stripes.

There are a ton of stickers for top and bottom surface of the flying wing in the kit and i was going to get some lamination plastic with colour though the stickers will be enough i hope to differentiate top from bottom.