Replacing furnace in single family house. Prefer replace existing 100k furnace with 100k furnace but existing furnace and A/C is 4 ton. New furnace is 100k but 5 ton. Can this work or am I going to have problems??

If the blower has more capacity on the new unit than the old it will work just fine. You might not need that 100,000 furnace since they were way oversized years ago. Instead I suggest you do a manual J on the structure and find out exactly what you need. With the new style high efficiency furnaces along with there higher output you usually do not need as large of a furnace to do the job. Furthermore if the new furnace is oversized it will create more energy usage and thus a much higher energy bill. Save yourself some $$$ and find out exactly what you need to start with.