Keep the tomatoes and the squash as far apart as possible.
Make a garden plan/map so you know where you planted everything so next year you can rotate your crops.
inter plant the onions with the tomatoes it's suppose to improve the taste of the tomatoes.
Get tomato cages for the tomatoes tall ones. Tomatoes love compost so mix about 50% compost with your garden soil to get the best crop.
onions do sucessive plantings so you have them throughout the year.
Get a bale of straw and plant the
potatoes in a raised bed and then cover it with several inches of straw. If the
potatoes raise above ground they will turn green and that part of the
potato is toxic. The straw will work as an extra layer covering the
potato.
Buy onion slips for any kind of bulb onion. Otherwise it takes two years for them to grow from
seed.
If you are planting green onions they can be planted as
seed.
seed tapes are probably best unless you can make yourself thin the rows. I never can. And if you are planting these definitely plant some this week and then wait two weeks and plant some more so that some will be ready 45 to 60 days from now and then throughout the season. I suggest you get the egyptian walking onion if you can. I got a few this year and I love them. Really nice flavor.
It is suggested that you buy
potatoes that are grown specifically for planting. That way there is less chance of them being blighted.
If your plot is small you may want to read up on horizontal gardening as concerns your squash. BTW squash is also a heavy feeder and likes a lot of compost incorporated in its soil and regular feedings of plant food.