The single picture doesn't give an idea of how much property you are being called on to care for so please indicate the total amount. Your strategy would be different if you're reigning in five acres or 1/2 acre. While planting some perennials in strategic locations could be nice, it should be limited until you see if living that kind of lifestyle is for you. It takes work and time. Nearest to the house would be the best place to start with that. I think the easiest care, best looking landscape that this could turn into is one in which the forest canopy is cleaned up. ... which means trim all the scruffy branches off of trees so that the trunks look clean and open and limb them up so that a view is maintained within the yard itself. Remove the scrawny saplings, shrubs and weeds. For the time being, kill the weeds with herbicide and mulch heavy with free mulch from the tree trimming companies. (Surely, there is tree trimming going on in the vicinity ...?!) (Invest in a backpack type sprayer as a carry type sprayer is not at all practical for a large property. You'll need good cutting tools (loppers, pruners, saw, etc.) Flimsy ones will not work well or last long. Mulch is good on a temporary basis, but a groundcover capable of large scale coverage is the best long term solution. Forget about the huge quotes. You can clean it up and get it under control for a few hundred dollars if you put it into low gear, be practical about it and persist. It is very easy to rid a property of poison ivy so you shouldn't let fear of it get in your way. Also, observe how others with large wooded lots are managing control of their properties. See what they're using for large scale groundcovers. Look especially at nice homes in the best neighborhoods.

The ivy I know sends out runners like a strawberry. If you 'pin' it down by resting a rock on the stem, then lightly cover it with some of your soft soil, it will probably send out roots and settle in. Keeping the area free of weeds may be tricky if you have trees nearby because the birds will deliver seeds for free. And, if you have neighbours with weedy yards, seeds can blow in from nearby. Be prepared to do some hand weeding for a while until the runners you're encouraging get going. I don't think I'd use any form of chemical control. The pitch on your slope indicates that there could be runoff and it just might have 'downslope' consequences. Keep your runners damp as they settle in and they will probably reward you rapidly. Particularly if you were to give them some liquid compost tea every three to four weeks over the growing season.

Endless Summer is not the name of a specific cultivar of hydrangea but rather of a series of reblooming hydrangeas. The one most folks refer to as "endless summer" is really Endless Summer - The Original, as it was the first in the series. Both Blushing Bride and Twist and Shout are Endless Summer hydrangeas - Twist and Shout IS a lacecap so that could be what you have. If it is part of the Endless Summer series (would have come in blue pot) then you should be able to prune now and still get flowers. Pruning hard now will remove the early flowering - those blossoms that develop on older growth - but you should still be able to realize flowering later in the season from the new growth. However, this new growth flowering does not seem to be 100% reliable for all the Endless Summer hydrangeas. Here is a link that might be useful: The Endless Summer collection

You can prune the bejeezus out of viburnum. If you do it right after they bloom, you should get enough new growth for bloom next year (on all the viburnums I have had, maybe not every variety). Plan your attack, get big loppers and a saw, and go to town.