As a rule of thumb the good moment to engineer is probably :
– If you can get use a significant edge in an activity that matters to you. Combat (CZ, RES, or frequent confrontations you don't escape from) probably is in this case of getting a significant edge, exploration often too (FSD range if reaching specific places matters). Seriously consider if the better metrics of engineered modules would get you that edge. Most of the time, earning time wil help (like more munitions means less re stocking, or – you don't want to trade anymore if I read you right but – more jump range would help for most trading loops, etc.).
– Engineering makes sense when you have a ship you will use in its current configuration from now on (or at least 80% of the time), which probably (1) you will keep the ship, (2) it is A-rated (D or others in some specific cases). This calls the question of wether you want to use the ship for a given activity (you like using for it, will probably do the activty often or at least come back to it). That's not a problem to engineer a Python even if you probably will end up using other ships for combat or missions, it is to engineer your Type 9 if you are bothered to death by trade loops and will avoid trading from now on.
– If you travel often, you may want to engineer at least the FSD of your travel ship, exploration and/or the ships you move often.
You can do some preparatory work before :
– stock as much high grade ingredients (level 5 or 4) as you can on the way (managing stocks up or down with Material Traders) ; missions rewards get interesting for this so keep an eye on the board
– unlock the engineers, maybe even get raise your level with them ; at least you can keep an eye on certain unlocking possibilities on your way (if you are near some systems, pile up combat bonds, etc.)
– plan, buy and stock modules for your fleet, like FSDs, so you can engineer them when visiting Felicity without bringing each ship to Deciat.
In your case, if you go for bounty hunting, you will probably get a significant edge from engineering an A-rated Vulture : it kills faster (more money per hour !) and is easier to manage, may stand longer in combat strides, and is probably a ship you will want to keep (oh and a few extra LY extra range will really be welcome).
Oh and for making more money, consider :
– Following cops in RES sites, they will help you kill guys faster.
– Joining Power Play with a power which grants you more money from Bounty Hunting, or at least their bonused systems. ALD or even better Pranav Antal (it can get obscene with rank bonus too, it may have changed since but we used to make 12 millions per hour Bounty Hunting).
– Taking missions for killing ships of a crime faction in the system you hunt in ; as you will go to station to repair/restock/give in bounties, and kill their ships anyway, it's essentially free money.
– Keep an eye for the patching of the KWS, it used to mean something like 40% or 50% more money and will probably get back to along these lines (and with courtiers, won't take time to give in anymore).
– Trying things so that you learn to kill ships faster (like aiming reactors or power plant, or dropping the few tons of gold you brought when the first pirate asks), and learning combat tricks (always moving upward to keep on target and allow gimballed firing – also allows avoiding asteroids –, using secondary thrust like in some combat tutorials, staying short range and out of line of fire of each type of ship, FA Off, etc.)
– Try if you succeed to get better money per hour changing some parameters, like security of the system and grade of the RES, weapons you use (lasers for longer endurance, laser+mc for faster kills, fixed if you hit for more damage overall than with gimballed), puttting points into engines when moving from one target to the other, etc.
