So I've just started to collect again and I've massed quite a few models already, so I'm looking for what to get next that would be beneficial for me.

I think I should at least get 12-24 rangers and Borimir

I have:
7 Knights (1 standard bearer)
12 Archers of Minas Tirith
10 Warriors of Minas Tirith (swords&Shield)
10 Warriors of Minas Tirith (spears&Shield)
1 Standard Bearer on foot
Aragorn the King (mounted)
Isildur
9 Numenoreans (Swords&Shield)
3 Clansmen of Lamedon ( I liked the models and understand they're considered bad)

First thing to pick up if you haven't already would be the Hobbit Rules, and the Kingdoms of Men sourcebook.

You have some solid foundations for an army (although Isildur and numenorians, and Clansmen are from different army lists) but it is widely considered that Guard of the Fountain Court are one of the most competative units in the Minas Tirith Army. You will also need heroes to lead your warbands, I personally like Faramir, Boromir of the White Tower, Cirion and Damrod.

One of the advantages of Minas Tirith is low cost heroes like Beregond and Damrod who can lead warbands, which help balance your BIG heroes such as Boromir, or Aragorn the King.

I have the WOTR rulebook, is it still up to date? Another question was that would I be able to use the numenorians and Clansmen as Allies in my army? Also, thanks for the advice.

The clansmen aren't bad, they're just unpopular. I love the clansmen! However, I highly recommend using them with their leader angbor the fearless that way you get the effect of having a banner on your clansmen. Angbor really makes or breaks the clansmen since they're all using two-handers.

The WOTR rulebook, is sort of up to date, since it is a different game and barely played anymore. It is specificly for mass battles. Where the SBG game is continued and supported with the new Hobbit rulebook.
That is the book you need, from ebay you should be able to get the mini version quite affordable and it holds all the rules you need.

To get the profiles to use in the strategy battle game, you need the already mentioned kingdoms of men sourcebook

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Iron sharpens iron
So a friend sharpens his friend.
prov. 27:17

War of the Ring aka WOTR is a much different system than the Hobbit SBG.
Which version are you trying to build forces for?
I was with you until I saw the WOTR.

There are a couple threads/discussions on the demise and cost of WOTR.
Your going to need to make or find movement trays for WOTR.

Even more challenging is finding players for WOTR.

Personally, I have pretty much completely divested myself from WOTR.
With all the units I had, I was able to build a very diverse force for SBG.

I will also add that SBG is so simple to run.
My 6 year old and I ran a game Saturday night, for about 3 hours.
We did not finish, but he finished me off.
He scored 4 victory points to my 2.
And lost a lesser percentage of his forces.
I think he cheated! hahaha

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Trading Post: viewtopic.php?f=38&t=26745&p=339385#p339385

Drop the archers and get some rangers, F4 with spears, awesome, Lead with a cheap Damrod or if youve got spare points use Madril for the extra might.
Mount your cheap heroes if you can like Beregond and Forlong, makes them soooo much better