I reckon you're on pretty firm ground treating it as a roleplaying game with a tabletop element - the core of Inquisitor is, in my opinion, the development of unique, complex characters who challenge the standard 40K archetypes, and the telling of exciting stories. I've heard of GMs going so far as to combine elements of the Inquisitor rules with parts of the Dark Heresy system for a more detailed/immersive roleplay experience linking up their tabletop engagements, which you might want to look into as an idea... I do however get the impression that even the sort of short, fast-paced campaigns some Conclave members run at organised events tend to be strongly narrative-driven and involve detailed world-building beforehand, numerous bespoke NPCs and so on. At the other end of the scale, the rules also hybridise well enough with skirmish-style games like Necromunda or Killteam for campaigns focused largely on combat, for those who prefer that style, but I'd say the majority of Inquisitor groups focus on developing a shared narrative over the potential for PVP competition. Game balance, should one choose to pursue it as a concept, rests entirely in the hands of the individual GM, with the only universally accepted rule I'm aware of being that all characters should have individual backgrounds that fit into the 40K setting and feasibly explain any particularly exotic gear or skills they possess.
As I understand it, there are multiple schools of thought within the community as to what exactly the game's niche is and how it should be played, especially regarding a universal yardstick for power levels, to the extent that I don't think a full consensus will ever exist. At the end of the day, Inquisitor amounts to a flexible rules system for table-top combat between individuals in a three-dimensional environment. The extent to which one builds a detailed in-universe story around that is a matter of personal taste, but given you have experience with roleplaying games and an interest in the 40K setting, I'm sure you can see the appeal of going the extra mile. An empire of a million worlds, spread thinly across a galaxy full of intelligent alien species, with all the limitless weirdness of the Warp underpinning it all, allows for the creation of entire planets and star systems for the purpose of your story, and looming threats of apocalyptic destruction on a similarly vast scale should a worst-case scenario result. Providing one stays away from conceits like E.G. blowing up major "canon" planets on which the Imperium relies, there is pretty much no limit to what a GM can do in a campaign without breaking the setting - and if the GM wants to mess with the setting, there's nothing actually stopping them from opening a time portal back to the Horus Heresy, or moving the timeline forward to the year 50,000 and killing off the Emperor, providing the players are on board with the concept. On top of all that space and essentially limitless narrative freedom, there is such a wealth of source material around for almost every aspect of 40K that inspiration for an interesting campaign is rarely hard to find.
In conclusion, I'd say approaching Inquisitor with D&D-style mindset is a fine idea, and in fact a year of running roleplay sessions will probably serve you far better as an Inquisitor GM than any amount of experience with GW's competitive wargames would. From the sounds of things, you're already on the right track to get plenty out of it.
