The number of spots is fixed, unfortunately (even the advanced editor won't let me do otherwise), and laid out as follows in the FM17 version:

1 automatic CL group stage spot, 3 spots for the 4th qualifying round, 2 spots and the domestic cup winner for the 3rd qualifying round:

Spain, England, Germany, Italy, Brazil, Portugal, France, Argentina, Russia

1 automatic CL group stage spot, 2 spots for the 4th qualifying round, 2 spots and the domestic cup winner for the 3rd qualifying round:

Mexico, Netherlands, Uruguay, Belgium, Colombia, Chile, Croatia, USA, Switzerland, Ecuador, Poland, Czech Republic, Ivory Coast, Austria, Turkey, South Korea, Japan, Sweden, Ukraine, Denmark, Romania, Wales, Australia

1 spot for the 4th qualifying round, 2 spots and the domestic cup winner for the 2nd qualifying round:

Bosnia, Paraguay, Algeria, Ghana, Scotland, Greece, Tunisia, Slovakia, Cameroon, Egypt, Ireland, Norway, Serbia, Iceland, Iran, Nigeria, Venezuela, Slovenia, Northern Ireland, Peru, Albania, South Africa, Israel

2 spots and the domestic cup winner for the 2nd qualifying round:

Finland, Bulgaria, Bolivia, Zambia, Morocco, Cyprus, Hungary, Armenia, Estonia

2 spots in the 1st qualifying round:

Senegal, Montenegro, Burkina Faso, Honduras, Mali, Lithuania, Angola, Costa Rica, Macedonia, Latvia, Georgia, DR Congo, Congo, Saudi Arabia, Qatar, Belarus, Iraq, Togo, Cape Verde, Jamaica, Guinea, Bahrain, New Zealand, Trinidad and Tobago, China, Sudan, El Salvador, Uzbekistan, Oman, Moldova, North Korea, Kuwait, Benin, Guatemala, Uganda, Canada, Syria, Faroe Islands, Mozambique, Equatorial Guinea, Jordan, Cuba, Malta, Lebanon, UAE, Panama, India

1 spot in the 1st qualifying round:

All other FIFA members (in other words: all other countries in the DB except defunct, disputed, or the following: Bonaire, Martinique, Reunion, St. Pierre and Miquelon, Zanzibar, Micronesia, Kiribati, French Guiana, Sint Maarten, Mayotte, Northern Mariana Islands, Guadeloupe, Saint Martin, Wallis and Futuna Islands, Tuvalu). In particular, Gibraltar and Kosovo's champions now qualify from here.