Hi, I would recommend staying on the 700 size if you go for electric, or 800+ if you go for gasser (leave the nitro option in the drawer, it would be an expensive waste of time).
With the 700 electric you can achieve 40 mins of flight at average 70 km/h cruising speed. You won’t be able to perform any hard aerobatics but “aggressive” scale flight (through FPV) .
Currently the best option you would consider is the XLPower 700 (cheap but really nice and lightweight frame : http://www.xlpower-rc.com/prolist.asp?id=222), or a classic T-rex760.
I would not consider going beyond 700 class on the electric side, the mechanics are expensive, and so are large capacity batteries and motors.
On the gasser side, after Helibug shutdown, the choice left are rather expensive, but you will love filling up the tank(s) instead of charging batteries (and buying them, of course…) . Most probably you will have to do some research and DIY to build proper damping platform for the FPV camera, but I can assure you, it can be done and the results are as easy to fly and operate as the electric counterpart.
Here is a video of my 800Gasser FPV heli:
Here a video of my old maxi joker electric FPV heli:
Regarding FPV equipment, if you want to stay on analog VTX I recommend the following TBS groundstation (you can hook it up to the goggles you already have, I assume they have A/V in port):
with one of their 2.4GHz VTX :
Finally, I strongly recommend this :
It is mavlink compatible, so you get a nice bulletproof OSD (do not waste time with minimOSD things).