I am looking for advice on table and form design as they relate to database
performance.

I have a Main table with 48 fields.  To organize my data better and to
reduce the number of fields in the Main table, I created a Provider table (16
fields) and a Receiver table (16 fields).  Their relationships to the Main
table are 1 to 1.  There are 500 records in each table.  Also, I have a data
entry form with a query record based on these 3 tables.  Performance has been
good so far.

There has been a request to add 10 more fields.  Performance-wise, would you
recommend simply adding these new fields to the Main table or create another
table with a 1-to-1 relationship?

As for the data entry form, there is another request to add 3 new subforms,
each having a table record source with a 1-to-many relationship to the Main
table.  Each subform will display roughly 5 records (3 fields) per record in
the Main table.  Performance-wise, would you recommend simply adding these
subforms to my main data entry form or should I have the users click a button
that would open another form which contains these 3 subforms?  I’m concerned
about the main form’s load time.

I would greatly appreciate any input.