Over the years we tried pretty much everything to keep the deer out - non-electric and electric fencing and substances of a plethora of aromas, transistor radios, sweaty Tshirts - you name it, we tried it. The best chemical substance in our experience, Tree Guard, works great for ornamentals, but can't be used on edibles (it seems to go systemic and is so bitter that any produce harvested is inedible). We still have really good results with a device called a Scarecrow that is motion detector activated to shoot a jet of water at the offending mammal. We've used them for several years and are happy with the results....it is important to remember to turn them on (!!) and to ensure that the battery gets changed regularly. I was protecting the driveway garden with a single device, but the edge nibbles of a few nights ago caused me to install the second one....so far, so good.
I am no tomato disease expert, but it appears as though the most stubborn annual issues for us are Alternaria (Early Blight) and Fusarium Wilt, both caused by Fungi. Early Blight is showing up now - lower foliage (shaded from the sun, or tucked low on the plant or in the container) is particularly susceptible and it seems to work its way up the plant; look for dark patches with yellow at the margins. I am working to remove the lower foliage that gets wet when plants are bottom watered, or that doesn't get the direct drying sunlight. I am also using disinfected shears to remove infected foliage every few days...we shall see how well that works keeping the plants vigorous and slowing the upward spread of the disease.
Fusarium shows itself as actual wilting of a part of the plant, accompanied by bright yellow coloration. Think of this fungal disease as impacting the plant by turning off the plumbing - water can't move up into the impacted plant parts. My bleaching and disinfecting efforts of my pots, driveway surface, stakes, cages are made in an effort to avoid or at least slow the incidence of diseases. The fungal spores are certainly around, and the diseases are activated by moist, humid, warm conditions - they can also show up quite suddenly.
What to do about plant diseases is really an individual decision based upon your own gardening philosophy - spray or not spray, organic or chemical. It is worth spending some time on Google to educate yourself on the various tactics and options.
I've found this site to be a particularly useful one for dealing with tomato issues. Be aware, however, that determination of what is specifically troubling your tomato plant is not straight-forward, since many of the diseases present very similarly.
As far as what I've seen in my garden strolls to date - there is some spotty Early Blight, maybe a single incident of the beginnings of Fusarium on one plant, a bit of white fly on one tomato plant, and some aphids here and there....I did also see a very young fruit worm on a pepper leaf, and there is the usual collection of flea beetles on some of the eggplant. I saw my first Japanese Beetle on a Hibiscus plant, and a stink bug flew on to my leg the other day (foolish insect...it is no more!). Now that we are into summer conditions, everyone who gardens will be starting to enter the part of the season when increasing challenges present themselves. The other thing I've noticed is some blossom drop on this or that tomato - the conditions just were not quite right for pollination - though I also am finding quite a lot of fruit set.
Good luck, all - it is about to get even busier - trouble shooting, maintenance...and eventually, harvest!