formula that returns the contents of every fourth row, except when that row is empty

Here's what I'd like to do (I've tied myself in logical knots trying to figure out how, but someone may be able to help):

The sheet I've got has headings, then four pieces of information for each customer that are mostly duplicates - ie, cells b2, b3, b4 and b5 are all the same customer's first name.
Therefore I want a formula that will not show anything except rows 1, 2, and every 4th one thereafter (1,2,6,10,14 etc). This could be in a new sheet or in a different part of the same sheet.

I need this doing for definite, the second bit would be nice to have but i can work around it:
I want certain colums to behave differently - in column L, instead of just the cell we'd normally show (2,6, etc), I'd like that cell and the cell below it, concatenated. And in column R i'd like just the cell below the one that would normally be shown.

Many thanks in advance, hopefully that was clear, if not then feel free to ask questions

yes, that would be easier, here it is

in this example, lines 2-5 are one customer, 6-9 would be another, etc.

And what I've put in line 7 is the result I'd like to get from the customer above.

Thanks

Actually, for now just a formula that returns every fourth cell to its left would be fine - ie, b1=a4, b2=a8 etc
(i've tried potting in a few of these and dragging the results but it keeps making up its own strange patterns rather than just using every fourth cell)

again, hope this makes sense, etc