Hello Modcon,
For many years now, the EU has made car manufacturers carry out prescribed tests to establish the maximum towed weight each model can handle. Its not just about weight and power , there are several factors that have to be taken into account, and you mention one of them which is hill starts. and it means that similar classes of vehicle can have very different towing limits. An important example of this was the original Vauxhall Zaffira, where as a result of the EU tests the more powerful diesel engined version had a lower towing limit that the less powerful petrol version!.
Another more recent issue has been car manufacturers making vehicles ever more frugal, and that can compromise towing capabilities.
For many years there has been a generalised adage that you need 40bhp per tonne for reasonable towing, so I guess you will be better than that with your proposed outfit..
In terms of weigh ratio, the unladen weight of the i20's seems to be just over the tonne, so you with and 850kg caravan you will be close to the industry recommendation for novice caravanner's of 85%
A word of warning about using tow matching web sites and services, The don't always carry correct details about your car and caravan, so the results should only ever be considered to be guide, and not gospel, You need to verify that all the details they have and use are exactly the same as your vehicles. Similar models are not necessarily close enough as per my example of the Zaffira.
Good luck