Keyword based domain linking

Suppose I have a website booksforall.com for selling books(mostly harry potter ones)

Now i buy suppose domains like buyharrypotterbooks.com
harrypotterbooks.com harrypotterbookssale.com harrypotterbooks.in not for the purpose of backlinking but as an investment in some highly generic domains

Now i create 5 pages(with different content) on each additional site i purchased for each volume of the book mentioning its price, features, etc.

So i have 4x5=20 pages
Now i link these 20 pages to my original site.

Acoording to me
1.site relevency of all 4 additional domains increase
2.backlink count of main site increase
3.ranking of all 4 sites as well as main site in serps increase (all external factors remaining constant)

Now the question is
are my assumptions right ?
as the somains are hosted on same server with same registrar will it affect me ? negatively ?
is there any harmful effect of this ?
is there any other good effect of this ?

ok

i assume that my question is a bit confusing

i will put it in a simple way
i have 4 domain names--highly generic and keyword specific.
I bought those not for the purpose of making links but just for investment. Maybe they could fetch me good $$

Now instead of keeping these domains empty I would like to make 15-20 pages on each and link them back to my original site as they are in the same niche my main site is

So will this be useful? or useless ?

Waiting for response
Thanks

If the domains are all on the same ip block, there is the possibility of raising red flags with google and getting banned for creating link farms

now how do i know whether its on same p block ?
will choosing another host help me ?

Search engines like large sites with a lot of content. What you are attempting is a game, a game which splits Page Rank and Link Juice.

If you link those four sites amongst each other, where does their strength come from if they have no other links but themself? 0+0=0.

Say you can build links into each site and make them all have 20 links each with each site having a PR of 3.

Well one site with 20 pages, 80 links and a PR of 5 would be much better.

Think about what the big players do. Does microsoft have a separate website for each product? Do they have three websites all selling microsoft? Amazon? Ebay? no, they all have their content focused on one huge domain.

Now lets think brick and mortar, would you open four stores to sell Harry potter Books, or just one and pack it with all the Harry Potter stuff you can find...

Egol said it best, something to the effect that google is much more likely to Rank the whole book rather than one chapter

ok i got your point

the thing is that the domains have such generic names that they are generating traffic and ranking in serps already. Some linking and content may get it to #1. they are currently just a 1 page site. Now the point is not to link them with each other, but to make them all link to my MAIN SITE. As i have already bought these domains i would like to put them to some use instead of keeping them idle.

I am not splitting my site into different divisions but just i liked those domains so bought them and i really want to make use of them as those are related to my main site.

Thats what my point is. I think i made my post a little confusing.
And yes would the same ip block affect it ?? even if i have modified content on each site ?