You'll get winded if your sentences are consistently too long, and hyperventilate if they're too short. Vary the length and structure of sentences as the content dictates, to keep the pace of the story lively. There are always exceptions, of course, but generally it's best to pick a verb tense and stick with it. Don't confuse readers by switching back and forth between present and past tenses. There are other, more creative ways to weave in events from the past or present.
Many writers attempt to use the present tense to create a sense of immediacy.
The present tense is difficult to use, and because it is not often used in literature, can draw the reader from the imagery to the written word. The use of the past tense will not get in the way of bringing the reader into the moment. You don't have to start at the beginning and end at the end. You can start in the middle, then give us a little background to put the event in context before going forward. Or start at the end, if that's your strongest opening.