Creating an early stage email collector so that you can invite people to join your mailing list is entirely sensible, even if you don't yet have a newsletter to send.
There's no need at first to get into anything more complicated than just allowing people to give you their email address.
A free Apption account give you 1 widget (the email form) and 3 embed areas (the tip jar is one, I can have up to 2 more without needing to pay for Apption).
And should someone be feeling generous, perhaps because they find your content useful in some way, they can 'buy you a coffee' (or whatever works for you). This is also a free account. If you get a donation there's a 5% fee.