Synths-
 
Waldorf Nave is an excellent wavetable synth and much cheaper than the plugin version. Attack is good but a bit buggy sometimes.
Korg's iMS-20 isn't bad, it's not quite the same as my actual MS-20mini but worth looking at.
Arturia's iSEM is good, so is their iOS drum sequencer.
There's also a good EMS VCS emulation and Moog do a good sounding version of one of their old modular designs.
 
I don't think iPads are good DAW platforms (yet), but if you're inclined to go down that road Garageband is free, and there's also Cubasis and Korg's Gadget which is a simple synth-based setup. Propellerhead's Rebirth is a must if you're into making old-style 303/88/909 stuff.
 
There are a few apps that have already been mentioned that can be used as touch-surface controllers. If you use one you need to go into the iPad settings and switch off the multi-touch gestures while using the controller. Otherwise things like moving two or four faders at the same time get interpreted by the iPad as OS control gestures.

Cactus Music
We don't know what your set up is so how can we say!

I am really sorry. I should have mentioned that.
Regards
 

Thank you friends!
 
There are so many options you have suggested. I will take time to understand them one by one.
I have also got an Alesis IO Dock II with 5-pin MIDI IN & Out.
A Mac Mini with Sample Tank Max and Komplete 10 installed with Studio One 3 Artist version I got with Nector Keyboard controller. Komplete Audio 6 is attached to this.
 
My main PC have my most favourite Sonar Platinum and some VSTi's and Plug-ins. I am using Yamaha MG-16XU as its audio interface / Mixer.
 
MG 16XU is getting Mic, Output of Komplete Audio 6, Yamaha Motif Rack ES, TC Helicon VoiceLive Touch.
I can connect the IODock II output to this as well.
 
I don't have any arranger Keyboard for a long time and now I am missing that. Should I go for 1ManBand or similar?
 
Is there any iOS app that can send start/stop/Break/Intro/Fill1/Fill2/Variation1 etc to 1ManBand?
Or any arranger App that can take Yamaha/Roland/Korg styles as well as Keyboard controller input for chords and send as MIDI to external device(s) depending on port/channels or over LAN [I am using rptMIDI]?
 
I am using rptMIDI.
 
Thank you all once again.
Regards
Snehankur