That depends on the context, it is certainly an ablative.
Also, why does the future subjunctive not really exist (i.e. you have to use present sujunctive and future participle?)
Probably for the same reason English lacks a future subjunctive
Actually, Latin will occasionally employ the future active periphrastic with a subjunctive form of esse, effectively creating a future subjunctive periphrastic (e.g. placiturus sim)
How could you get a passive meaning of a deponant verb, like i was persued from inesquor, insequi, insecutus sum? Or would you have to use a different verb ( i know that deponants are passive in form but active in meaning)
A funny thing about Latin is that pretty much all of the possible synonyms for “to follow” are deponent. You are forced to use different constructions; rather than saying “the leader having been followed”, say “when (some) followed the leader” if temporal and “the leader whom (some) followed” if descriptive.
What nouns have a locotive case apart from domus and rus?
Textbooks usually say that the nouns with locative case are domus, rus, humus, towns, and small islands. There are actually a few others, such as animus (animi at heart), but not all of them were realized to be locatives by the Romans themselves. They will also sometimes employ an apparent locative (e.g. castris) for reasons that are unclear to scholars.
Why does fugere have a supine but effugere does not?
Different sources will sometimes list a supine and others will not. In my dictionary, effugere does have a supine stem.
I have formed a new group of verb- 3rd special- indicative present active 1st person singular ends in io like effugio, behaves like group 4 verb mostly- is it a good idea to keep this case?
I am confused 
Gerundives can be of attraction or obligation, does this apply to gerunds?
( I don’t suppose it does as gerunds are verbal nouns not verbal adjectives)
No, gerunds do not express obligation. Something like tenendi means “of holding”, never “of having to hold”.
Is it better to use abfui or afui for the perfect of absum, abesse?
Both are acceptable. The compound adsum, adesse also has the alternative forms affui, affuturus.