So many good questions – thanks for sharing these. Taking a bit at a time, I would like to mull over your first two for a bit, hoping that you might find a clarifying insight.
Evidence of the empirical sort is something that we value to take us as far as it can reach. And when empirical evidence has reached the end of its leash, but important questions still remain we (some of us) consider a wider body of evidence that comes from collective and individual human experience (testimony). This is evidence of the “taste and see” sort. Just as with empirical evidence, it isn’t infallible – and with much harder questions. It isn’t blind to the empirical sorts of evidence, in fact including, even subsuming it for the thinking religious person. There are those Christians who do wish to dictate what the empirical evidence must find and how it must be interpreted. They are willing to dismiss it if it doesn’t meet their expectations. But there are a great many of us that find that to be an unsatisfactory and highly fallible addition to the gospel message. And every step of the way, whether trying to stay just within the stricter empirical evidence or evaluating all the evidence –faith is the backbone of it all. Nobody escapes this contra to what so many try to spin here. People can deny it, but that only cripples their self-reflection and leaves their faith dangerously un-examined. But we all have faith in something, and it is 100% unsupported (by definition) because those parts that we can see by opening our eyes is no longer faith but knowledge. God gave us good minds to use. We walk by the daylight for as far as that will take us. That is taken for granted – hence the needed reminder in Hebrews [corrective edit: this is from 2 Corinthians (not Hebrews)] that “we walk by faith, not by sight”. I take this to mean that where the questions of life and love really start getting interesting and important, then it is where (in whom rather) our faith is placed that becomes really, really important and our sight cannot take us all the way. It doesn’t mean we should gouge out our eyes and then beg for direction. We use our eyes for all they’re worth and then realize that they are not everything and nor can they be. Faith was always there too, and for some things it is faith alone.
So think of evidence as your “starter kit” toward helping you incubate a relationship of trust with your creator. The bible doesn’t shy away from inviting us to “taste and see”. Some even get inspired by the stricter empirical kind, but problems arise when they want to live there and want that evidence alone to deliver them all the way to the promise land. They want to go the whole way laboring under the idea that faith and trust need not ever be involved. But when that fails, their faith [in God] flounders and their real faith commitments are revealed. Be careful what you have set your spiritual sights on. Is your faith in Christianity? or Christ? The first may simply be the trappings of a religion, or set of doctrinal propositions, a certain way that Scripture must be read, a whole body of things --some useful toward turning your view to Christ and maybe a whole lot to distract away from Christ. The latter --faith in Christ is a relationship with a person, involving trust, love, devotion, study, … lots of things that Christ produces in us when we are found in him. He precedes them all – they don’t [of themselves] lead us to him.
The notion of “Christianity being true” is already a strange one as you might have gathered from what I said above. As a religion “Christianity” includes an impressive array of extra-biblical writings, creeds, prophecies, convictions, and every manner of notion. Given that many Christian denominations may have put forward exclusive claims about this or that, I guess we would have to say there must be falsehoods there, right? At this point the agenda-driven anti-theist is satisfied that his biases are confirmed, and he walks away. This would be about like us approaching science with the question: was France right? or Germany? And even when we find faulty scientific conjectures in the history of both nations, we don’t then dismiss all science as bunk. The question itself is absurd because these are nations with histories involving a myriad of minds. Even narrowing down to just one French or German person still requires us that we focus in on one proposition authored by that person before we can begin to address truth or falsehood. So there will not be any major world religion with all the complexity entailed within that can manage to get everything wrong. Nor will any of them get everything right. And in any case, this is pretending that the word truth (when we speak of it religiously) refers merely to a set of propositions.
So to be fair to your question then, you probably are really asking is Christ our one True lord (where Truth is something more than a mere proposition, though it certainly includes that at its core). Here is one short answer I propose as a Christian: Christ is True. Religions just are. Is this my unreliable human reason talking? It sure is. I want to use it for all it’s worth, but I have to learn to trust Christ in the midst of my fallible reasoning and also for the rest where my reasoning can’t reach. Whatever denomination or even religion then follows (or preceded that according to your birth circumstances) is neither here nor there, but is destined to be considered part of Paul’s proverbial “rubble” given over that we may know Christ. Some or much of it may even be redeemed as Christ comes to reign. Other parts changed or driven away. And that will apply to the religion that now goes by the name “Christianity” along with everything else.
May Christ make himself real to you and strengthen and encourage you, and all of us to heed his call together.