Hey OP, Psychedelic veteran here. My .02 on your questions:
>A) Will I freak out if I do it by myself when my wife is out of town?
Would you 'freak out' if you had done mushrooms by yourself when your wife was out of town? Dosage varies, but you can roughly equate 3.5 gr of mushrooms to 150-200 mics of LSD. For your first time, take 100 mics. You'll probably be fine unless you're emotionally unstable and unable to soothe yourself on your own.
>B) How long does it last? Can I do anything at all while I'm on it, or am I basically turned into a vegetable that needs to stay on the couch?
Again, this depends on dosage. @ 100 mics, you should still be very functional, and probably very full of energy. You may be a little 'loose', 'sloppy', or 'silly' in the way you go about things, so better to be around either people you know will be fine with it, or nobody at all. But yeah, you'll still be functional. It usually lasts 10-12 hours in total, but the majority of the intense part will be the first 4-5 hours. After that, it's a long slow taper off of it. Come downs are great for reflecting.
>C) Any tips to ensure a good, pleasant experience?
Set & Setting. Make sure you're in a good space mentally, and make sure you're surrounded in a place where you feel comfortable, free from judgement, and able to express yourself with ease. LSD tends to make a person much more sensitive to their surroundings, and much more suggestible. I like to kind of set up a bunch of music, books, blankets, etc before I go for it so that I'm all ready to just rock. Tripping alone is fun for me. But then again, I'm an introvert.
>Keep in mind that I get really paranoid when I smoke weed. Maybe I should just not try the LSD?
You know, it works on different brain receptors. I get paranoid on weed too (or at least I used to), but I rarely if ever do on acid. Granted, I've learned how to 'let go' into the LSD exprience, which is the golden rule of acid: Surrender to the experience.