To Upgrade from Vsphere 4.1 to 5.1

Right now we have single vc(vm)..Managing multiple datacenters.. Under which we also have 2 dc running on 3.5.
So in 1st phase we are planning to upgrade the datacenter running on 4.1 only.
What we are planning here is..Now-to create another vc(vm) ..then move all current infra to new vc except the dc:(datacenter )running on 4.1 only.
Then we will proceed with vc upgrade
So my concern is..Any additional license required for new vc to manage current whole infra having 3.5/4.1 on it?
Any concern related to ssl/cert..We have to create/transfer..On vc?
 And how upgrade manager ll be used ..on both vc..as patching is also going on in whole virtual environment?
Then after vc-will upgrade host to 5.1 then –vm upgrade-data store upgrade from 3.1 to 5.1,
Any limitation /downtime for Datastores upgrade from 3.1 to 5.1?
Any other precaution we have to follow?

Thanks @hanccocka ..for all ur assistance here, wll update you accordingly.

1st we have to check the same in test environment..then ll share my findings

here my query  is how..we have to manage with snapshot/template..during migration?

and earlier query regarding any cert/ssl dependency during migration?

also please share the best practice we have to follow during migration from 4.1 to 5.1

we would need same[template/snap] to be migrated  to 5.1..so how we have to proceed ?

And will vmware view upgrade [current version 4.0.1]cause any problem..here ,as we have one cluster running for vdi only..so we would need to upgrade..that ..to make it compatible  with 5.1?

 will it cause any issue/any dependency?

we have plan to execute everything first in Test environment..so will it required additional licence for VC or any other support. we would need in test environment or if any evaluation licence will work here?

In test plan .what we have planned will take 2 physical boxes as we have in our prod environment

our plan is...

build test(VM)  for vc-then will deploy test database server(vm) -get this db configured-Install Vc 4.1

then will go for test esxi/esx 4.1 installation on 2 test boxes(physical)
>will create test datacenter - test cluster-then  will add host to vc cluster..and assign storage to both host
>will create test vm./template on these hosts
> ll create new vm for another vc...to support out of scope environment..which will not be taken care in this migration
>configuring update manager to preform the upgrade from 4.1 to 5.1

is there something we are missing here to test before migration?

It  is our business requirement to get it implemented before going to prod migration.

Any San/Network team dependency..?

Any third party plugin like for storage/vmware..we have to upgrade with this migration?

Thanks.

is there any specific need to extend space on storage also when migrating from 4.1 to 5.1..

like for Vc/vc database/VMFS upgrade...

Extended storage space not required.

when going to upgrade vc from 4.1 to 5.1..is it required to extend ram as well?

we also have to upgrade vmware view 4.0 to 5.1..any limitation  for this?

we also have to upgrade vmware view 4.0 to 5.1..any limitation  for this?

I'm afraid that's a new question.

ok, actually it covers..all in vmware upgrade for my current setup..

np, can ask in another question thanks for all the info provided here

Thanks a lot