I have had a look on Google Maps & have seen quite a few roads near Old Trafford for off road parking.
Can anyone confirm the parking please.

Theres a lot of on-street parking around the Trafford Hotel pub.

What about going by train from warrington or tram from Altringham?
How easy is it? How direct?

Ordsall Lane has loads of parking, especially the top end towards Regent Road. No more than a ten minute walk to Old Trafford.

Could always park at Trafford Centre and walk up

Ordsall Lane is full of double yellow lines.

I was thinking of Trafford Wharf Road / Warren Bruce Road.

the imperial war museum has a massive carpark right by it

Secure parking is available for 160 cars, including designated parking spaces for Blue Badge holders. These cannot be reserved and are available on a first-come, first-served basis(charges apply). The car park fills up quickly at weekends and during holidays, so we advise that people arrive early. The following charges apply:

0-3 hours £4.00
3-4 hours £5.00
4-6 hours £7.00

As you get towards Old Trafford there are loads of guys in Hi Vis jackets directing people onto warehouse loading bays - usually £5 parking fee

Park on the cricket ground, cheap and a short walk to the ground.

where is the best place to park near OT and how much is it?

Free on street parking near Trafford Park station (15 minutes walk) or around the corner from Trafford Bar tram station (10 minutes walk)

When United play, there are plenty of parking spots around the back of White City up to Trafford Bar starting at a fiver.