I'm interested in the Holy Terra (or around) and Segmentum Solar defence forces.
A Segmentum is really pretty big. Even if Solar is the "smallest" one.
I know that The Solar Sector is guarded by Battlefleet Solar, the mightiest Battlefleet of the Imperial Navy (Lexicanum
But what I want to know is what Astartes Chapers and Imperial Guard Regiments operate mainly. This excludes the Grey Knights and Inquisition forces because they operate everywhere in the Emperor's Galaxy.
The same is true for Space Marines and Imperial Guard. They operate everywhere. PLus you forgot to mention the Adeptus Mechanicus, Mars and a couple of other important Forge Worlds are in the Segmentum Solar.
For a list of planets in this Segmentum see for example here:
So you already have Armageddon, Catachan and Necromunda in this segmentum. Check what forces fought in the wars for Armageddon, then you'll have a partial list of who operates here.
Then you can check what links to Segmentum Solar:
I am not going to fish out all Astartes chapters now, you can do that yourself, this was just to show that by using the tools provided by the Lexicanum you will be able to compile a quite comprehensive list.
Does The Holy Terra have some planetary defence force similar to the planetary guard of other Imperial Planets (the main source of recruits for the Imperial Guard).
Good question. Probably but I can't think of a reference right now. But I think i remembered reading somewhere that Terra was exempted from tithes.
Does have his own Imperial Guard regiment/s?
Maybe. There are (were) the 5th Armored Terran Praefects
. Although if they were really founded on Terra or if it's just some kind of honorific title is unknown. Also mentioned were the 4th Terran Praefects and somewhere there is a mention of the 1st Terran tank Division.