Firstly with a pwBPD
I have decided to give her the benefit of the doubt, and try and trust what she says
This can never be a given, and cannot be guaranteed. It is more allowing yourself to accept what she says rather than outright trust. The difference is that importance shouldn't hinge on it being the absolute untwisted truth. What a pwBPD says is just a vehicle for expressing what they feel and obtainiing what they want, absence of absolute truth and honesty is a core problem with BPD.
To survive a BPD relationship you need to come to terms with the reality that what you hear is not absolute.
I want a relationship where my SO is willing and capable to come visit me.
To obtain this you will have to decide what you want to do, rather than attempting to persuade (control) what she does. She will make up every excuse in the world to get you to make all the effort if she can. Dont engage in this. You say this is what you are going to do. Leave it at that if she wants to see you more she is quite capable of determining whether she is going to make the effort or not. As long as you are "negotiating" solutions she wil just keep throwing up excuses.
I found life a lot easier when I dont put my partner in a position were she is pressured into coming up with reasons, setting myself up to be told a lie if you like. If you do this eventually you wont even believe them if they are telling the truth. I believe what I see or hear for myself, all else is just interesting, neither believing nor disbelieving, dont get bogged in the details
This the beginning of the RS, she will make more effort now than later, so be careful about "giving" too much, as it will slide into the expectation that you will always compromise
I'm sorry, but actions speak louder than word
This is true but words do create a good smoke screen, and if if sling enough mud some of it will stick, and you will believe some of it. This is one of the reasons you stay away from negotiations and asking for reasons. Stick to this is what "I" am going to do. It is up to her to add any extra contributions, you cannot extract them from her.
So, to my question regarding boundaries. Is it acceptable for me to work out a plan between the 2 of us where we agree to seeing each other a set amount of times a week, and alternate with who comes to which town? I want her to be part of this plan, but at the same time if she claims that she can't do it, I will have to say goodbye. A basic personal need will not be met.
Your boundary is to say how often you are willing to visit and leave it at that, if you cant deal with whatever input she makes then you end it isf that is how you feel. The idea is to take the "demand" part out of it, that implies controlling and will be met with instinctive stubbornness and then portraying you as bad.
Negotiated or pressured actions on her behalf will not be consistent, and are likely to be overridden down the track. If she has not desire to do this so wont in the long run. Sense of responsibility and fairness are often alien to a BPD mind
In short do as much as YOU are truly happy to do without reward.