“ The information Im getting on the internet is that I should take out the existing converter, because the inverter is a charger/ats.“
There is no reason whatsoever to disable your OEM converter-charger...The Aims manual list this unit as a ‘inverter-charger’ rather than a ‘converter-charger’ (though it’s charger function may well suffice as a converter...). If you ‘opt’ to use the Aims charger instead of the OEM converter, simply switch off the converter breaker at the main panel... This will give you the added flexibility (redundancy) of using either charger OR both concurrently, assuming your battery bank is capable - note also that the Aims charger’s amp output is user adjustable as is the battery type...
As far as you question about the secondary ATS Switch goes, in order for shore power to ‘pass-thru’ the inverter, the inverter must be switched to ‘ON’ , and when ON there's about a 3.5amp continuous parasitical drain from the battery bank...A second ATS switch negates this need to have the inverter switched to ON (to route shore power) because it provides an secondary-alternate path into the main panel...
Without this alternate path you would need to leave the charger section ON (either the Aims or OEM converter) to simultaneously resolve for this parasitic drain ...Note that once the inverter is switched ON, you can then choose to have the charger section of the inverter ON of OFF, or switch on the existing OEM converter at the main panel...
BTW, the cable run you mention = 12’ round trip, thus to fully utilize the capability of your inverter (surge rating) you should consider using heavier cables - at a minimum I would suggest 2 aught or greater...
