I'd go with a spray acrylic or polyurethane clear coat. The spray will give you the smoothest finish on furniture, and will also eliminate the risk of smearing your designs on the off chance that the paint hasn't completely cured yet. Demi-gloss and high gloss will both give you a good shine, but since high gloss has a tendency to show every little surface scratch I usually go for the demi. Be sure not to overcoat, as a too-thick coating will get wavy and crack over time. And finally, just like with paint, you want to try and work on a low-humidity day so it cures quickly and properly.

The clearest, most durable finish that won't alter the color of your designs would be one of the water-based polyurethane or acrylic finishes like these:

http://www.minw…

http://www.rust…

They look a bit cloudy while wet, but don't panic; they dry crystal clear and are very tough finishes. They'll be perfectly compatible with the acrylic you already have on there. One issue with them is that they will tend to trap air bubbles if brushed on, but it sounds like you've got a lot of design action going on, so a few little bubbles shouldn't be too conspicuous.

I think both of the above products are available through Home Desperate...er, I mean Depot.

this would be the same spray you would use as an after finish spray on ceramics. I have used this on wood peices as a finiah coat.

If you used acrylic paint you don't have to worry about ruining or smearing the designs, as long as you paint is thoroughly dry. One thing you MIGHT have to worry about, though, is that spray paint basecoat you used. If you use a spray varnish now, there is a possibility that that the two sprays might be incompatible and the varnish will cause the basecoat spray to bubble up and peel. You don't want that! Sometimes if you use the same brand of varnish and basecoat spray, you will be ok. But it's a real risk if you use two different brands of spray like that. I have had it happen, and it ruined the project.

So, what I would do is head to the craft store, like Michaels. You will see bottles of liquid varnish, in the brands of Decoart Americana or Delta. Decide if you want matte of gloss. I would put a couple of coats on this to help protect the surface, and maybe even more on the table top. Another product I use and recommend is Mod Podge. I use it on almost everything I paint, if I don't spray it with the Decoart Spray Varnish. Mod Podge is a bit thicker and adds even more protection for your painting. If you live in a hot and humid place though, you might find it a bit tacky for the chairs.

Good luck! I hope you used some of my designs on the table!! LOL!