1. The pump should be mounted close to the tank. They don't much like to suck fuel, just push it. Easiest to use a VK/VL/VN V8 mounting bracket. You will also need a tank that has a "swirl pot" in it +/or a low pressure feed pump +/or an external swirl pot to get fuel to the EFI pump inlet. If it's in a VK. there's no need to reinvent the wheel; you can use the EFI VK tank and pumps, a VL tank and pumps or, with reference to the recent thread, a VN-VR tank and pump (note the singular for the pump, applicable to VN-VR other than VN V8). Later than Series I VP have the return line in the sender which is better because the spigot for the return line tends to get broken off the earlier tanks.
2. There's no need to provide any assistance to the fuel return and while the pressure regulator could still work effectively with doing that, it may not.
3. Referring specifically to the external VN V8, VL (and VK) pumps: The problem is there's no such thing as a 'VL' or 'VN' pump. Within the same external package there are a number of pumps. To a great extent they are interchangeable and parts retailers prefer to keep a single pump that can cover a variety of applications. Bosch makes available online a catalogue with fuel pump flow ratings at standardised pressure. You might like to reference that for flow ratings.
Using the VN-VR tank means only a single pump is needed and it's in the tank. A VN-VR V8 puts out from 165kW to 215kW (HSV - so maybe upgraded pump). Realistically, even S/C, how much power do you think you are going to get out of your 3.3? If the pump will meet the fuel flow rate of a factory engine at your anticipated power output and an allowance for operating against boost pressure, it will be OK.
If you want to do some ballpark figures as a check: petrol density is ~760g/l = 0.76kg/l, energy content is ~43MJ/kg, thermal efficiency is likely to be around 25-30% (lower when you have to drive a S/C, so use maybe closer to 20% or a guess on S/C power consumption as below), 1MJ = 1000kJ, 1kW = 1kJ/sec. From that you can estimate the fuel flow rate required to met a particular (anticipated) power output.
eg. 150kW = 150 kJ/s = 25% x 43MJ/kg x 1000kJ/MJ x 0.76kg/l x 'X' l/s and solve for 'X'.
'X' l/s= (150kJ/s)/(0.25 x 43MJ/kg x 1000kJ/MJ x 0.76kg/l)
= 0.0184l/s
x 60s/min = 1.1l/min
Add in a margin for error for fuel enrichment (you can factor that in explicitly if you want to; use 1/Lambda or use a nominal stoichiometric 14.7:1 divided by a typical air:fuel ratio, say 12:1) and flow losses in the lines etc., say a factor of 2 or 3, and you have the required flow rate for a naturally aspirated engine.
The S/C draws power which has to come from the engine (which you will have to provide fuel for but will never see at the flywheel). Calculating that is possible but might be something like 20kW at a realistic boost pressure so add that onto your anticipated power output.
That you are running boost will affect the flow rate of a particular pump. The relationship is non-linear; a square function. Doubling the fuel flow rate requires 4 times (= 2 squared) the pressure; double the pressure and the fuel flow rate increases by only 1.4 x (= the square root of 2). So, the capability of the pumps to provide flow diminishes with pressure above the rated pressure. Use Bernoulli to get a rough estimate of how. I'll let you look that up online. You can ignore the static and friction head terms and just equate the pressure and flow rate terms: low, rated, pressure to the new, high, pressure with boost.
You can, and should, check your actual fuel flow by measuring the fuel flow out of the regulator with the engine off, with, if you're running boost, the pressure on the fuel pressure regulator reference hose (normally connected to the manifold) increased to whatever boost pressure you will be running. A big ass medical syringe pushed into the manifold hose works but you'll need to measure the fuel pressure - best, provided you know the reg. pressure, typ. 250kPa above manifold pressure but easily measured as a check - or air pressure in the hose.
4. The rated flow of injectors is likewise provided by Bosch in their catalogues. You know your required fuel flow rate from above (without the arbitrary "factor of 2 or 3" but with the fuel enrichment consideration). Simple maths: 6 x "rated fuel flow rate". It's a general guide to keep injector duty cycles below 80% so x 0.8. (The pressure difference across the injectors is constant due to the fuel pressure regulator referenced against manifold pressure so there's no need to allow for extra pressure with boost.)
You might also want to check what your engine management system needs wrt injector impedance. There are two types: high, typically 12-16 ohms when measured with an Ohmmeter, low, maybe 1-3 Ohms. They are not interchangeable. VN are high, VK?? but also probably high.
