ふるさと納税 – Need clarity on the process (first-timer)

I want to get clarity on how Furusato nozei works and the conditions that I need to be aware of.
I briefly had a look on the wiki that has a detailed guide on FN but its kind of a lot to go through at once. In the mean time, I'd like to get your thoughts on the following questions.

I checked this website that provides an estimate of how much one can spend based on factors like annual salary, dependants, social insurance etc. ( I understand this may not accurately reflect the limit)
https://www.furusato-tax.jp/about/simulation

In my understanding, I can spend this estimated amount for FN in the current calendar year ( Jan-Dec 2024) and claim it back during the tax returns on the next calendar year(March 2025). Is that correct?

Considering this, I need clarity on the following:

1. The estimation seems to depend on the Resident tax (住民税) as well. In my case, I joined a company last April after graduation and I received a mail from the tax office stating that I'll be paying 住民税 from this year July. So, my question is even in this case, can I assume that if I enter my annual salary, insurace details etc, I can spend the estimated amount shown in the above link?
2. During the estimation, should I also account for the bonus and other incomes that I may receive or just the base salary of this year? My understanding is any taxable income is considered including bonus. (Just don't want to overestimate the amount I can spend.)

Appreciate if you could provide some tips/recommendations on how to make the best use of the ふるさと納税 system! Thanks!