I have completed a 1 year business plan for my startup. Should I do a 2-3 year plan as well?

Craig is right, you'll need 3-5 year (you might aswell do 5 year btw) financial projections; a spreadsheet of course, with summary yearly costs/EDITDA etc on a slide in your deck.

The plan can take the form of a slide deck. Use something like this as a template:

10 to 15 Slides

COMPANY PURPOSE

Define the company/business in a single declarative sentence.

PROBLEM

Describe the pain of the customer (or the customer’s customer).
Outline how the customer addresses the issue today.

SOLUTION

Demonstrate your company’s value proposition to make the customer’s life better.
Show where your product physically sits.
Provide use cases.

WHY NOW

Set-up the historical evolution of your category.
Define recent trends that make your solution possible.

MARKET SIZE

Identify/profile the customer you cater to.
Calculate the TAM (top down), SAM (bottoms up) and SOM.

GROWTH
Go to market strategy
If viral, why will it be viral? ('Sharing' is not an answer)

COMPETITION

List competitors
List competitive advantages
What is your unfair advantage?

PRODUCT

Product line-up (form factor, functionality, features, architecture, intellectual property).
Development roadmap.

BUSINESS MODEL

Revenue model
Pricing
Average account size and/or lifetime value, LTV
Sales & distribution model, CPA & CAC
Customer/pipeline list/status

TEAM

Founders & Management
Board of Directors, and any key Advisors

FINANCIALS

P&L
Balance sheet
Investment to date
The deal (EXCLUDING valuation OR completion date)

AND financial projections/cashflow (as excel s/sheet, ideally 5 yrs but atleast 3)

** You'll also need, for review before investment (due diligence): **
- Company formation docs, any trademark, patent, etc certificates
- CAP table (current shareholder ownership to two decimal places %
- Contracts of employment (Founders should have these also, and you should have founder vesting agreements)
- IP assignments for employees/contracts current & previous if not included in their employment contracts
- Any insurances, atleast the minimal required by law (i.e. in UK employers liability if you employ anyone, public liability insurance if members of the public visit you at your place of work or if you perform work at places of work owned by third parties, and Professional negligence, not mandatory but sensible (covers you for eg. making a mistake in a piece of work for a customer, Loss of documents or data, Unintentional breach of copyright and/or confidentiality, Defamation and libel, Loss of goods or money, your own or for which you are responsible).
- In the UK, registration with the https://ico.org.uk/ (illegal not to if you store peoples data)

Slide headings based on an amended list from Sequoia.

Long typed out business plans cloud the precision that data and specifics provide. A deck as above with few words, forces you to get to the crux of your business and your go to market strategy and will be valuable both internally to you and your team and of course to raise funding.

If you can't make it concise and clear, you probably have not thought it through enough.

If your business plan is for the purpose of raising money, then funding sources will want to see 3-5 years of financial projections as well as market information that will support those numbers. I would need to know what your definition of "business plan" is.

If you look up typical business plan templates, you can find the items that should be in a business plan; however, 20 and 30 page business plans rarely get read. I suggest no more than 10-12 pages of what funders want to know to lend or invest money.

If you would like assistance on this, feel free to contact me as I have prepared many business plans and pitch decks.

Best of luck,
Craig

Most likely no. A single business plan is enough. The key is to make sure that what you actually wrote is good. And if you are a first time entrepreneur, you have little way of verifying whether what you planned will actually play out. This is where you have toget advice of experts to go over your plan.

Just build the site and generate traction first. You need only 90 day plan. Validate the business model. Then build the app. This will take a few months. Now write the business plan and you would have developed enough confidence in the business model and the numbers can be corroborated.
When you do, write the plan for 3 years as that will help you clarify your expansion strategies and plans.