Geoscape Strategy (Hardmode)
As Hardmode assumes the player is familiar with vanilla X-COM, this strategy section will detail additional strategic issues, tips and tricks that Hardmode presents. Generic strategy information pertinent to vanilla X-COM can be found here: https://www.ufopaedia.org/index.php/Category:Tactics
Consider reading the 'X-COM Base' page for a overview of some effective base designs: https://www.ufopaedia.org/index.php/X-COM_Bases_(Hardmode)
Financial constraints are far more considerable in Hardmode than in vanilla. In the early game even $500k is critical. The first base X-COM constructs is freely built, specifically the cost for the access lift which is dependant on the region it is placed. Vital regions to ensure are covered include Europe, North America and Asia, and as base locations in these areas are expensive it may be prudent to place your first base in these regions to save on funds later down the line. These regions also cover your strongest financial contributors thus ensuring their protection will help defend your finances in the early game.
Eventually X-COM will want to ensure global radar coverage, having multiple strike teams across the globe will also increase resource recovery rate, response time and also decrease the impact of troop losses. Losing 5 soldiers when you only have one team of 30 soldiers is far more punishing than if you have a multiple teams of almost 100 soldiers (give or take) across the world.
Your first constructed base is well designed and defendable, with good expansion potential, you will likely need to expand your storage and living space capabilities at first however.
X-COM needs four things to operate effectively, it needs more radar coverage, troop strike capability, research space and manufacturing space. A single base will not fulfil these needs for long. Early expansion may prove vital and the sooner this begins, the faster a base can come online.
Having multiple strike teams may have been a luxury in vanilla X-COM, but in hardmode this may now be nessecity. Constructing bases that will house interceptors alongside a contingent of soldiers performing missions will not only improve your global response, but also ensure your ability to defend your strike base from alien retaliation missions.
Due to the changes to research times, you will need a lot of scientists. A dedicated research base will likely prove necessary, a base holding at least 150 to 200 scientists, plus 50 to 100 from your starter base, should prove sufficient for the entire game.
Consider placing this base in a remote location and avoid engaging any UFO's near it to avoid retaliation missions against it.
As financial issues will be a pressing concern through the campaign, a dedicated manufacturing base with a large engineering staff will be vitally important for keeping X-COM afloat. This base can also serve as a storage base to accumulate the large excess of alien artefacts that X-COM will accrue.
As with research bases, consider building this area in a remote area and avoid drawing UFO attention to it.
Research and Development
Recommended around 200 to 250 scientists to remain on top of research...
Council of funding nations income will quickly become insufficient to meet X-COM's financial needs, must suppliment with selling alien assets and manufacturing items...
The Air War
Pros versus cons of intercepting UFOs, alien retaliation risks, discussion on aircraft regarding effective ship and weapon types (Retailator being a big boon to X-COM and Laser Cannon's being actually useful)