I don't know much about bush cucumbers, hopefully somebody else can help you.

5 gallons is what I consider minimum for tomatoes. You're planning on using 4 gallon pots with some of the space taken up by a water reservoir? That's really tough.

Celebrity is not an option (in my opinion). Though determinate, it is famous for a vigorous/explosive habit... it will outgrow the pot within a month.

Focus on the varieties meant for container gardening - Patio, "Bush" varieties, "Dwarf" varieties, Tumbling Tom, Sophie's Choice - you should be able to find much more complete lists with keywords like "dwarf", "patio", "mini", "short", etc.

IMO 4 gal should be ok. I'd definitely try it. A little bigger would be better, but if that's what ya got, go for it. I grow decent sized tomato plants in 5 gal. containers.

The smaller the container the more attention will be required with regard to watering, feeding, too much heat on roots, etc. Likely, you will get some tomatoes. I agree that in the future you might want to look into dwarf types.