Re: What's a "normal" number of guitars to own?
Really all you need to do is explain or let her hear the difference in sound between the strat and the LP. That is enough of a difference to make you want it right?
Just yesterday I went to youtube to show my wife some demo's of the (5) pedals I am building at the moment. She could hear the difference between them and could understand that I would want to build them. (Ok it's more difficult to show the difference between a fuzz and a fuzz or a distortion and a distortion, but I just happen to be building a compressor, booster, overdrive, fuzz and autowah).
The same way with guitars. I currently own 1 acoustic (the first guitar I bought, about 10 years ago a takamine EG523SC), one american fender strat (cheap find for 400 euro's including a frontman 212 amp) and a G&L ASAT tele (with the P90 like pickups, got it almost new from a friend for 250 euro's I think), also a bass because I played bass for a year with a gig I did, but I lended that one to a friend who is learning to play it. I of course would love to add a couple, like a LP, a PRS type, a thinline Tele, a 335 type, a cheap floyder etc. Just to have them, have the flavors available to me when I like and just because I love guitars. I would love to build a couple of them myself, build my own amp and maybe just for fun a violin. I tell my wife these things, she gets used to it and I am pretty shure over the next couple of years I get to buy or build some of these ones. We just plan the finances, do the saving for all sorts of stuff and then it is really no problem at all, she actually enjoys seeing me enjoy this stuff, so what more can you ask for

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I guess the key really is showing that she means the most to you, that you'll take care of her, put her first, that you prioritize taking care of the kids, the house etc., that will usually make room for a lot of goodwill in my experience. When she feels loved and taken care off, she'll gladly see you enjoy some new stuff. When she feels you are putting this guitar stuff first... not so much...
Ah well I guess I digress a little bit, the answer to your question would for me be up to 7-10 max if it is just a hobby/every now and then a gig/praise and worship band thing. If you make a living of off it: as much as you need. If you are rich enough and will not get into trouble for it: as much as you want... For me the 'normal' amount depends on the importance of it in your life and on the circumstances of your life really.