I will repeat just the topic of each question.
Question: 1) Is there such a vipaka sukha (sapa) vedana for even an arahant that he experiences?
Pleasant and unpleasant vedana that come through the body (kaya vinnana) are kamma vipaka (due to good/bad kamma done in the past). Those are called sukha and dukkha vedana. Even Arahants (and the Buddha) experienced those.
Vedana coming through the other four physical sense inputs are neutral. Any pleasant or unpleasant vedana that we may experience are ALL mind-made, and NOT due to kamma vipaka. They are called “samphassa ja vedana”. They are also called “somanassa/domanassa vedana”. Arahant DO NOT experience those.
– See, “Vēdanā (Feelings) Arise in Two Ways”
– Also see, “Difference between Phassa and Samphassa”
By the way, I highly recommend the series of posts on “Paticca Samuppada in Plain English”
Question: 2) The pleasure that “comes our way”. Is it still bound to our gathi?
Whatever somanassa/domanassa vedana that we make on our own are due to our gathi (or gati). An Arahant has removed all gati and does not experience those ‘samphassa ja vedana” per the above explanation.
Your comment, “it is only attractive because of our gathi. But this process of our defilements coming up as manosankhara does not create kamma.” It is not fully correct. There are some kamma vipaka due to mano sankhara that arise even with vipaka vinnana. But they cannot bring rebirth. So, I may not have specified that.
– When we start doing vaci sankhara and kaya sankhara (those are done CONSCIOUSLY), that is when we generate strong kamma that can lead to rebirths.
You wrote, “Only once we start with sankalpita rāga (which happens from the time it turns to vaci sankhara which happens pretty much immediately after the Avyakata PS has run – IF there is gathi).”
– That is correct.
– By the way, “sankalpita raga” are vaci sankhara (talking to oneself). That will become clear if you read the posts mentioned under question #1.
I am not sure what you mean by, “So again I am confused how this concept of sukha/dukha vedana that comes from dhamma loka and even an arahant experiences fits in.”
– Please feel free to re-phrase that part, if it is not resolved from the above explanation.