This is the loadout I use with great success. All you need to do is turn off the Cargo Hatch, and you're good to go. I believe you can fit a 4C fuel scoop on there as well, if you put the FSD on a lower priority. You might be able to squeeze in something else, too.
During combat, I'll general keep 1 pip in Systems to keep a slow but steady shield regen., 1 pip in Engines, and the rest in weapons. If I get on a local mob's bad side and find myself getting randomly attacked, I'll tend to keep 2 pips in Systems for that little bit of extra defense from surprises, and the rest in weapons. I can also tell you it's common for other CMDRs to use 2 pips in engines and the rest in Weapons.
To clarify about power priorities: the higher the number is on a specific module's priority setting, the lower priority that module is. A priority 1 module can stay online when a priority 2 isn't.
Always keep your Cargo Hatch on a priority of 4 or 5, depending on how you have your priorities set up - whatever the lowest is. Your Cargo Hatch is about useless when you're in combat and have weapons deployed. You also can't use your FSD with weapons deployed anyway, so set that low as well (I keep FSD at 4 and Cargo Hatch at 5, personally). If your ship needs more power when you deploy weapons, it will go up the list from lowest priority to highest and turn things off until enough power is allocated.
If you're having problems with certain modules going offline unexpectedly, I can think of two things:
Turning off your lower priority systems still isn't freeing up enough power. If your power is overclocked at 110%, and you turn off the Cargo Hatch, you're still at 107% power which will continue turn off higher priority systems until you're down to 100%.
The Vulture is the ship with which you will have the most problems managing power. You will not be able to have everything you want on it.
You may have organized your priority setup differently than you intended. This is less likely to be the case, but just double-check your important things are in 1st place and the unimportant things are in last.
Also remember - if you lose shields from buying a new shield module or turning it off, etc., they don't turn back on immediately and will take some time to recharge.
There are a lot of Vulture builds around, and a lot of threads have tons of advice. If you search this sub for "Vulture," you'll find a lot more help, especially in regards to builds and power management.