Good Paid Windows apps for my new Windows 8.1 tablet

I have purchased a Dell Venue 8 Pro recently and I have $25 voucher for the Windows app store.

I am new to the Windows apps scene and my online searches for finding the best apps for this tablet have given me very poor results. So now I'm hoping the Microsoft Tribe will help me out a bit :)

I have shied away from tablets so far but the allure of using an active stylus for note taking and making me productive made me bite the bullet and buy a Windows tablet. (I'm yet to get the stylus as it was out of stock).

Not really keen on games unless they are exceptionally good.

I'm looking for:

1. Awesome note taking apps (other than OneNote and Journal) to make full use of the stylus.

2. Apps which could help programmers / developers.

3. Good File manager

4. ??

Thanks in advance :)