1. Main support beam is sagging in the basement.
= A lally column or two might freeze this in place. Reversing it might cause new problems - doors that have long since been adjusted to fit the sag might not like no sag, etc.

2. No ventilation in the attic, moisture present. Upstairs bathroom vent terminates in attic, no soffit baffles.
= Definitely needs repair. If you use that bathroom vent in the winter, the ceiling will rain in the spring.

3. Boiler is pretty well aged and warrants replacement based on age alone.
= It might last 15 minutes or 15 years. Cannot predict.

4. Garage roof is sagging.
= Sistering up some of the rafters might freeze or even reverse this.

5. None of the outlets GFCI work with a trip tester.
= Easy to replace, but get a second opinion with a different tester since NONE of them tested good.