If we take the standard married filing jointly deduction and claim our 3 children, I will owe about 20-25,000 in taxes.

If you sell, figure 10% in selling expenses so if it sells for $100k, you only get to keep $90k minus the existing mortgage.Depending on how much your house has appreciated/ will appreciate by the time you are ready sell, capital gain taxes will need to be considered (up to $500k may be excluded if married so long as you owner occupied for 2 out of 5 immediately preceding years). 

Yes me and my fiancé(getting married in April) have discussions on getting started in real estate almost on a daily basis.

If you’re married You have to have more than $27,700  in expenses before you save 20-40% of dollar 1. 

Some form of management agreement stating the terms of how the property is managed, should accompany the TIC agreement if you go this direction.Keep it simple to start and get a deal or two under your belt with your investor before you "get married" with a grand plan.  

What is the relationship like regarding how the government views an LLC if it's run by a married couple?

Luckily, even better than a 1031 and DEFERRED taxes is primary home exemption ($250k for single, $500k married filing jointly) . 

On your fourth point-- it's important to remember that just because someone is your partner on one deal, doesn't mean you're married to them.

Primary 2 out of 5 years up to $500,000 gain for married.  

Although I will say before I got married, I was renting rooms and I have a few friends who travel together, so they look for larger properties and just split the cost.