That is always the best use case of these tools. Find things for humans to use their expertise on.
dumples
I don't think the tarp will help with anything while its below freezing. Typically the tarps is used to increase the temperature, remove sunlight to kill the plants and if it gets hot enough to kill all weed seeds. So I doubt that will help before its below freezing. I have used it before to kill some weeds but that was late august. It won't be hot enough and will act similarity to snow.
The best method would be to do Sheet Mulching which is similar to what you are planning on doing but not 100%. I would start with a layer of cardboard, followed up by mulch / leaf litter and then finalize with compost. I would plant my plants directly in the compost and then cover in straw. You won't need the silage tarp because the cardboard weed layer should stop the grass and most of the ivy from growing. It will also start composting which the tarp will not. Around the edges the ivy can survive since the shared roots pass sugars from anything outside of the cardboard.
I have used sheet mulching to create two different small garden over the last few years. I started mine in the fall and planted in the spring which worked well. I have done it now for our second year for our vegetable garden along side some no / low dig methods. Last year was our first full year and our garden was thriving without any amendments. I expect even better results this year as soon as we can start planting.
I have been DMing a campaign for the last few years that has downtime as an instrumental part of game play. Basically they run 2-3 adventures each month with the remainder of the 4 weeks of the month doing downtime activity. So I have some advice to make it fun and get the players involved.
First off I would look at the DMG, Xanathars Guide to Everything and Acquisition Inc source books because they all have rules for running downtime. That includes charging for lifestyle expenses and methods to make money. I would use those as the basis for what you are going to have the players do. The basics are do activity, risk money, make skill check(s) and get something back if pass or lose it if failure. What I do is just ask the players what they want to do and then debate / collaborate to getting this tied into one of the options. I wouldn't do it weekly as suggested in the book but rather a few times. That way the players can change their world this their two years and maybe make or lose (just as fun) money.
As for the ritual spells the wizard could realistically get all of those spells if they had the money (they likely don't) or the time (which they will). So I would use the spell scrolls costs to allow them to buy whatever scrolls they want and then copy it in the book. If realistically they can't buy the scrolls they might need to get charged extra to import it or spend time traveling to a larger city to buy them both of which will cost them extra. The amount of gold they have will limit what they can buy.
Just note that while its possible to get lots of lower level ritual spells with time the costs for higher level spells gets difficult to purchase. The wizard should be spending their money on spells and getting scrolls and spell books are fun for wizard players.
If you are worried about they using it make sure to track time in dungeons and other locations. It takes 10 minutes to cast these spells which eats into durations for other spells. I also make sure I account for time to move through a dungeon. I use 120 ft. (4x movement speed on average) for new territory for 10 minutes. They can move faster (10x) over terrain they have covered before since they aren't on the lookout for traps and monsters. I even roll for random monsters if appropriate in dungeons (typically 5-10% chance for one to appear) which forces people to take time into account. Its way more fun because they have to balance things. Do they want to keep their hour long spell up or waste their last 10 minutes casting Detect Magic as a ritual. These are fun decisions for a player to make.
What I would do is to give everyone an amount of gold pieces that they can use during this downtime. I would also make sure to charge them to live style expenses as well or net that out to zero is you are assuming they are working for their living. With this gold give set costs for each spell scroll (I would do it by level) and then the player can choose what they want to do with it. Get new ritual spells or keep the gold or upgrade equipment
Anytime my player use their actions and resources to interact with the world as of it's real I like to support it. I in turn treat the world real back which is what the player wants to do. We like to talk it through to make sure it feels fair to both of us.
For this example where your player is pouring oil and lighting a weapon rack on fire. So I would tell them that the oil will become visible once poured. So I would do a stealth check to get it lite. And either 1d4 rounds until the notice or give the enemy a check each round. Its fun to have these back and forth
I read it somewhere so it makes sense there is a source besides trust me bro.
Also logically everything has been under snow for months. What are a few more weeks under a tarp? You might get things to germinate quicker but that's it.
Edit: I'm sure I read it from the U of M the first time