Yes, in regards to AFVs, wider tracks will help in marshy terrain. However even lighter AFVs will tend to be road bound. As well as limited to ops in urban areas if the area is at all built up with a hard deck. Like in many cases in Op Market-Garden in the Fall of '44. Generally the armor vs. mobility question is an old one. And I'd go for a balance in design. Also note like in WWII ops around Antwerp and the Netherlands, as well as in French Indo-China after WWII. Many Amtracks were used as well, like the Buffalo LVT and in Indo-China the Weasel also ...
http://www.ghqmodels.com/store/united-s ... craft.html ...
http://www.ghqmodels.com/store/united-s ... bians.html As well, the US did use a few HoverCraft in the Mekong Delta region of Vietnam in the '60s, the PACV.
http://www.ghqmodels.com/store/vietnam- ... erine.html Note all those vehicles mentioned were lightly armed and armored ... Both the French And US used armored more heavily armed Riverine forces in shallow draft river monitors and landing craft as well ... Also as noted Spec Ops(Scuba/SEAL) and well trained Infantry in rubber boats like the old RB-15s and more modern Zodiacs would also be affective. I've been deployed by USMC Amtracks [LVTP 7s]
http://www.ghqmodels.com/store/united-s ... racks.html , USN/ US Army LCMs, RB-15s and Zodiacs as well USN River Patrol Boats [known as Swift Boats]. The US also ran PBRs like seen in the movie Apocalyse Now. So I'd think light armor with tracks or wheels, possibly with deep fording capabilities [even our M113 APC was design to swim as both Europe and even the ROK is full of streams and rivers]. Arming some of these light vehicles with as big as a weapon as it can be mounted like in a version of US ARMY Stryker* or USMC LAV. These series of vehicles have APC, mortar, AT, etc. versions, and even a * direct fire version making it a light "tank" so to speak.
http://www.ghqmodels.com/store/modern-u ... -lavs.html And don't forget, Helicopters both transport and gunships can be vey useful, in all terrain. And note even lighter FA can be mounted on LCMs and be used as mobile fire support platforms. So certainly have some good FA as well as AAA/ADA in your Forces ... Your infantry should be armed with all the standard weapons : ARs, MGs, GLs, Shoulder fired AT and AA, sniper rifles and light mortars ... For Log support vehicles like the WWII DUKW and the modern LCACs would be useful. And you will need some aircraft to provide CAP and CAS. But Air Superiority or even Air Parity may be hard based on your enemies' capabilities.