What amount of amps should i have

There are a lot of issues that need to be addressed before anybody can offer a guess.
It will be hard for anybody to give you a solid answer.
Numbers of A/Cs or heaters, oven, water heaters, lighting and lots more.
Port, stb, for & aft service inlets, transfer switches, service inlet breakers, GFI, Galvanic isolators, generators, chargers, inverters and bonding.
You have to realize that you will be on this boat, using it and probably sleeping on it, maybe swimming around it. Family and friends included.
With that in mind, there is no short cut or cheap way to do this. Especially when lives may depend on it.
Please consult a surveyor or marine electrical consultant.

Most modern boats of that size in the US would have one 50 amp/240 volt power connection. ( I'll probably get pushback on the voltage nomenclature , but in my experience, it's supplied at 208-240 volts). Maybe two, if you have some unusually high power uses, but I've never seen any boat with three power cords.

In general, you'll use the 240 for a water heater, cooktop, HVAC units and pump, and maybe a battery charger. The lines then get split down to 2 x 120 v legs that power everything else.

Please keep in mind that there are very specific requirement for wiring aboard a boat. This in not like wiring your home. not a job for an amateur.

On a boat that size 120/240-50 is the way to go although some may suggest twin 120-30 as you may not have or need any 240 loads

Multiple inlets may be an overkill on a 40 footer. The purpose is to reach shore power whether you are how in or stern in etc. if installing two inlets they will both feed a single panel using a rotary selector switch to select which one is used

As others mentioned their are guidelines and rules you need to follow for safety and also so your boat pass survey and is insurable.

Ours is 50A/240V but we have no 220-240V appliances. The main supply is split into two 120V legs and everything runs on one or the other of those. We have spare capacity.

I've seen some boats (few, not most) in this size range with a single panel but two inlets, one fore and one aft... presumably to add some flexibility when trying to reach shorepower connections.

-Chris

Good luck getting a qualified sparky to come in and mess with your DIY stuff. When you have problems who will be responsible? No offense, but from your posts you sound wholly unqualified to do what you're going to be doing.

Our system isn't particularly divided by area or location. Instead, the loads are balanced so each leg handles approximately the same amount of load. One fridge on each leg, on AC on each leg, cooktop on one leg and convection oven/microwave on the other, charger on one leg and water heater on the other, etc etc etc.

And usually things like nav lights, electronics, exterior and some (most?) interior lighting and so forth would be DC loads, different animal from your AC side.

Your marine electrician ought to be able to balance AC and DC loads easily enough...

Ideally, have your pro designs your system first, have him specify wire sizes, ideally you both will pay attention to color codes s for future troubleshooting... and have him agree to what he wants you to pull where... before you start pulling or even buying wire. You only save money on the grunt work by doing it yourself if you do it right, ideally the first time.

-Chris