combining INDIRECT in one formula?

[Smellyelly]

Apologies in advance; I'm sure this question has been asked before, but I don't know how to search for it in the forums, as I don't really know how to ask what I'm looking for. Please feel free to delete this thread if someone can offer advice on what I should search for and I can see if there's existing threads which answer my question.

The gist of it is this -

Question 1a - this is a stripped down version of what I'm looking to do, but should point me in the right direction

I'm looking to combine/nest multiple INDIRECT functions in one single formula...I think.

Let's say I have a range of values in cells from A1:A100

In cell B1 is the value "A1"

In cell B2 is the value "A100"

In cell B3 is the value "A"

In cell B4 is the value "1"

In cell B5 is the value "100"

I know that I can write a formula that says =AVERAGE(INDIRECT(B1):INDIRECT(B2)) which will return the average for my range in column A.

But is there a way to combine multiple INDIRECT functions into a formula such that I could write it something like =AVERAGE(INDIRECT(INDIRECT(B3)&INDIRECT(B4))&":"&INDIRECT(INDIRECT(B3)&INDIRECT(B5)))

Or put another way, am I able to write a formula which can run an INDIRECT formula that combines values from multiple cells?

Question 1b - if the above is possible in some way, I've got a next part of the question which would involve doing that but pulling data from another worksheet tab, but I'll save that for now

Thank you for any help or suggestions you might have!