Have I been too nice/ accommodating?
Absolutely not. Being "nice" is (almost) never wrong. Being "accommodating" is (almost) never a bad idea. You seem specifically concerned about how "nice" you were when scheduling the interviews - I think we can completely ignore your "niceness" in terms of scheduling interviews, because it's a total non-issue in the bigger picture. Discussing dates and being flexible on interview times is just a normal part of the process, it wouldn't be seen as extra nice or different.
That said, I do think you may have made a mistake, although it has nothing to do with being nice. You said:
they asked me about my salary expectations so I honestly informed them about the range I'm expecting and added that I was open to negotiation
If your primary concern is landing a specific desired salary, and that salary was the bottom number in your range, you're probably in the right ballpark. If your concern was getting the most money possible, then yes - you absolutely made a mistake.
Most employers have a range or a target salary in mind for a position - typically it's the maximum they're willing to pay. When they interview, they want to know your desired salary for one (or both) of these purposes:
- If your desired salary is way above their number, they don't want to waste their time interviewing you, under the assumption that you wouldn't take their offer.
- If your desired salary is way below their number, they now know that they can save money by offering you your desired salary instead of the number they already budgeted for.
If your number fell into the first bucket, they wouldn't have scheduled the interview. So, by default, you now know that there's a very high chance that you're basically going to be offered less than their maximum number, even if the offer is within your desired range. To put it another way: You may get the number you want, but it probably won't be the highest possible number you could have gotten from them.
There's lots of good advice on the internet and on this very site about negotiating during the hiring process. Most people recommend giving a generic answer to questions like "what is your desired salary" in order to avoid being short-changed. You should read up before you continue your job hunt. It may be too late to salvage this offer, but you will be better off in the future if you're prepared before you start the negotiation versus coming and asking for help after you're halfway through it.
Here are some questions on this site you should look at. None of these are exact duplicates of your question but they all have some relevance. Taking an hour to read and prepare for negotiation can make a huge difference, it may be one of the most valuable hours of your process in terms of return on investment.
Is it advisable to negotiate salary during job offer even after answering the salary expectation question?
Does the first person to mention a number in a salary negotiation lose?
How to negotiate salary when range is unknown
How to negotiate salary with an extremely unprofessional in-house recruiter?
How to negotiate a job offer effectively during and after an interview
How to counter questions about expected salary? [duplicate]
How to respond to a direct ask of salary earned and expectations?
How to negotiate a better salary in a job offer when the recruiter says that he or she does not want to create a salary imbalance within the company?