repair "family crest" bought in 1966 London, paint is dripping

​A client asked me to repair a family crest he bought or had made in London in 1966. Some of the paint is dripping — not sagging. It looks like thick liquid paint dripped a few inches. 
There are areas on the surface where the paint is tacky but most areas are smooth.

My understanding is that the dripping happened in recent years after he moved it to his house. The object does get direct sunlight so my guess is that heat has caused the problem. 
​I did some solvent tests to try to figure out what kind of paint was used — Isopropyl Alchohol dissolves the paint fairly easily so I removed all the dripped paint though a combination of cutting the thick drips away and then using the alchohol to remove the rest. 

​I have a limited amount of time that I can spend on this due to his budget and have already applied a fresh layer of acrylic over an area that I removed the dripped paint. 

My questions are: 

1. Is my plan to overpaint with acrylic artist paint ok for this purpose? (I use Golden acrylic for my own work.)  

2. should I varnish, and if so what kind of varnish would be best since I don’t know for sure what kind of original paint was used. I have both MSA and Polymer varnish from Golden.

3. is there anything I can do about the tacky areas or should I remove those areas and repaint them also.

4. any ideas on what caused the paint to drip and how he could avoid this in the future? (I will advise him to keep it out of the sun!)

The paint looks like enamel paint and the object looks like it may have been a sort of tourist purchase. I don’t have much of a budget for this project,so I need to do the best I can in 3-4 hours. I am a painter, not a conservator.

Some more information about this piece:

The painted plaque has relief decorations and is mounted on wood with screws through the back.  It appears to be some sort of thin plastic molded over a thin piece of flat wood, with the hollow areas filled with a dark brown resin like substance that looks dry and porous.

thanks for any insights, suggestions, advice!