Depending on how much weight it will be lifting you could use iPower 2217-Q or if you need a lot of lift the 2814-Q with a set of 30amp ESCs reflashed with SimonK firmware. I've found APC thin electric props to be very good performers on the DJI stuff, very similar blade profile to Graupner but come in a much wider range of sizes and pitch. I have several different OSDs on my FPV quads and the best bang for the buck I would have to say is the Remzibi. If money is no obect then the EZOSD gives you pretty much everything you need on a multi. I have both Remzibi and EZOSD flying and I like both, the Remzibi is a bit more useful if you're going long distance, not usually much of a consideration on a quad though.
The Immersion FPV gear is very good I use it almost exclusively and it's all I use on the 5.8 frequency. My usual setup is a 600mw 5.8 Immersion with a skew planar wheel on the TX and an Immersion Duo 5.8 diversity using either a combo of a SPW and crosshair or a pair of crosshairs 180 degrees apart for coverage of long fields. I've found the SPW on the TX side with at least one crosshair on the RX side to be the best all around setup for 5.8 FPV on a multirotor, I get clearer video with no dropouts where the cloverleaf 3 lobe will glitch a bit when turning, that extra lobe on the SPW does make a difference.
As far as extending the landing legs, I typically use 5 or 6 mm carbon fiber rod cut to whatever length I want and tire wrapped to the outer edge of the landing leg on the DJI arm so they angle inward. A couple layers of heatshrink over the bottom end to give it some more diameter to sit on and that's it, cheap and easy to fix though it does tend to break easily on a rough landing but I'd rather that than an arm or something more expensive to replace. If you want to carry a camera underneath there are a lot of choices but the Aeroxcraft is as good as any, I have one of their 2 axis GoPro gimbals and it's well worth the asking price.
For FPV can the F450 centerplates and get a set of the TBS Discovery frame plates for it, here's what it looks like with the iPower motors, reflashed ESCs, EZOSD, and the Immersion FPV gear. Since this pic I swapped to APC props and the SPW antenna, flys great and it's now my favorite quad and my ultimate F450!
Ken
