Using Arrays and Keyword fields

I want a set of fields to track actions a contact took on a campaign: 3
controls, for Action Date, Campaign, and Action, plus a large read-only box
below that. A user enters those 3 pieces of info, and they are stored in
keyword fields. When that contact is next opened, the read-only box would
show in 1 row the date, campaign, and action last entered. Over time it
would show the 4 most recent sets, and you could scroll down to see earlier.

I think I could have unbound controls for Action Date, Campaign, and Action.
When the form is saved, the new action is appended to the end of the Action
keyword field, and so on. When the form is opened, I Split the keyword
fields into arrays, then display them in reverse order in my read-only box.

--How do I write code to append each new value to the end of each keyword
field (I could Split each kw field into an array; is there some way to say
array=array+newaction, then Join back into the kw field?).

--How do I put the most recent values, at the end of each keyword field, at
the top of the read-only box?

--What would make this even better is if the unbound controls for Campaign
and Action were combo boxes filled with previous values from those keyword
fields, so instead of retyping "Clean Air," I just select that from the
list. But if that contact has already done 3 actions on Clean Air, how do I
keep the list of campaigns in the unbound control from showing Clean Air 3
times?

Many thanks, Adam