Since you haven't specified your budget or displacement cap, recommending something accurately won't be possible. So we will give you a bunch of options across different displacement and price brackets. The type of machine that will best meet all your criteria is an adventure bike. At the lower end of the spectrum, you can take a look at the TVS Apache RTX 300, which has all the features you want and then some in its top-spec BTO guise. 

One step above that would be bikes like the KTM 390 Adventure models and the Royal Enfield Himalayan 450, which are excellent all-rounders at pretty decent price points. 

If you can stretch for it - and since this is your final bike purchase, we would strongly recommend you do - the Honda NX500 makes a serious case for itself. With its twin-cylinder engine, it will have the obvious refinement advantage over the other bikes mentioned here. It is also a machine that has cemented its reputation for reliability and low ownership costs over time. Also, it checks the feature and riding experience boxes that you are looking for. 

That being said, it would be advisable to take a test ride of each bike and see which one suits you best before making a decision.  

The Honda NX500 is a smooth, proven, and reliable package as an ADV tourer, and is something you can't go wrong with. Its few drawbacks are its steep price tag and a shock that rebounds a little too quickly for comfort. Since it's a Honda bike, it's likely to last a long time without major issues and also be fairly easy on the wallet to maintain. 

Since we have not ridden the BMW F 450 GS, we can't comment on its strengths or weaknesses. We recommend you wait until the media as well as owners' reviews of this bike are out before making a purchase. 

If you want an adventure bike that is E20 compliant, you will need to either purchase a new bike or search the pre-owned market for a lightly used model manufactured within the last 1 or 2 years. 

If you are looking for a new bike, we would recommend paying the high initial purchase price of the twin-cylinder Honda NX500. It is a rather sorted machine in almost every regard and will feel like a nice step up from your single-cylinder KTM. And since you're familiar with the trouble-free Honda big bike ownership experience, the NX500 makes for a logical step up. 

If you decide to go for something a little less pricey, then bikes like the latest KTM 390 Adventure models and the Royal Enfield Himalayan 450 are also options worth looking at. 

You also have the option of waiting for the new BMW F 450 GS, although its pricing will be similar to the Honda bike rather than the single-cylinder models mentioned above.

A test ride of everything you shortlist should help you make a decision. 

There's no way to accurately portray how much the maintainance cost of the BMW F 450 GS will be, as it is yet to be launched. However, BMW bikes have a reputation for being a little pricey to live with, even the smaller 310s. You shouldn't expect the F 450 GS to be as easy on the wallet as its peers, like the Royal Enfield Himalayan 450, KTM 390 Adventure models or even the Honda NX500. 

We recommend you wait a while before you buy the F 450 GS so that you can see thorough reviews of the bike. Also, you can speak to actual owners of the machine, and then make an informed decision.